Ankit

Arduino Height Measurement System

Ankit Chapagain — Tue, 03 Nov 2026 16:59:55 GMT

1. Project Overview

The Arduino-based Height Measurement System uses an ultrasonic sensor to measure the distance between the sensor and a person's head.

The sensor is mounted at a fixed height, facing downward. When a person stands beneath it, the system measures the distance from the sensor to the person's head.

Python calculates the person's height using the following formula:

Person's Height = Sensor Mounting Height − Measured Distance

Technologies Used

Arduino UNO
HC-SR04 Ultrasonic Sensor
Arduino IDE
Python
Flask
PySerial
HTML, CSS and JavaScript

System Architecture

       HC-SR04 Sensor
              |
              v
          Arduino UNO
              |
              v
     USB Serial Communication
              |
              v
       Python Flask Server
              |
              v
       Height Calculation
              |
              v
        Web Dashboard
              |
              v
       Display Height (cm)

2. Hardware Requirements

Component	Quantity
Arduino UNO	1
HC-SR04 Ultrasonic Sensor	1
Jumper Wires	4
USB Cable	1
Computer/Laptop	1
Fixed mounting frame	1

3. Hardware Connections

HC-SR04 to Arduino UNO

HC-SR04 Pin	Arduino UNO
VCC	5V
GND	GND
TRIG	Digital Pin 9
ECHO	Digital Pin 10

Sensor Installation:

Mount the ultrasonic sensor horizontally at a fixed height.
The sensor must face vertically downward.
Keep the sensor stable.
The person should stand directly below the sensor.
Measure the distance from the sensor's ultrasonic face to the floor.

For example:

       HC-SR04 SENSOR
       (Fixed Position)
       ┌─────────────┐
       │             │
       └─────────────┘
              |
              |
              |  Measured Distance
              |
           _______
          /       \
         |  HEAD   |
         |         |
         | PERSON  |
         |         |
         |         |
         |         |
         |_________|

       ----------------
             FLOOR

Example:

Sensor mounting height = 200 cm
Distance from sensor to head = 30 cm

Person's height:

[ H=200-30 ]

[ \boxed{H=170\text{ cm}} ]

Important: The sensor mounting height must be measured accurately from the sensor's measuring face to the floor.

4. Arduino IDE Setup

Step 1: Install Arduino IDE

Download Arduino IDE:

https://www.arduino.cc/en/software

Install and open Arduino IDE.

Step 2: Arduino Code

The following program measures the distance using the HC-SR04 sensor and sends the measurement to Python through serial communication.

No additional Arduino library is required.

// HC-SR04 Configuration

#define TRIG_PIN 9
#define ECHO_PIN 10

void setup() {

    // Start serial communication
    Serial.begin(9600);

    // Configure sensor pins
    pinMode(TRIG_PIN, OUTPUT);
    pinMode(ECHO_PIN, INPUT);
}

void loop() {

    // Send ultrasonic trigger pulse
    digitalWrite(TRIG_PIN, LOW);
    delayMicroseconds(2);

    digitalWrite(TRIG_PIN, HIGH);
    delayMicroseconds(10);

    digitalWrite(TRIG_PIN, LOW);

    // Read echo duration
    long duration = pulseIn(ECHO_PIN, HIGH, 30000);

    if (duration == 0) {

        Serial.println("ERROR");

    }
    else {

        // Calculate distance in centimeters
        float distance = duration * 0.0343 / 2;

        // Send distance to Python
        Serial.println(distance);
    }

    delay(500);
}

Step 3: Upload the Program

Connect Arduino UNO to your computer.
Select the correct board: Arduino UNO.
Select the correct COM port.
Upload the program.
Check the Serial Monitor at 9600 baud.

Expected output:

These values represent the measured distance between the sensor and the person's head.

5. Python Environment Setup

Step 1: Install Python

Download Python:

https://www.python.org/downloads/

Verify installation:

python --version

Step 2: Create Project Folder

Open PowerShell or Command Prompt.

mkdir Height_Measurement
cd Height_Measurement

Step 3: Create Python Virtual Environment

python -m venv venv

Step 4: Activate Virtual Environment

Windows PowerShell:

.\venv\Scripts\Activate.ps1

If PowerShell blocks activation:

Set-ExecutionPolicy -Scope Process -ExecutionPolicy Bypass

Then activate again:

.\venv\Scripts\Activate.ps1

Windows Command Prompt:

venv\Scripts\activate.bat

After activation, you should see:

(venv) C:\...\Height_Measurement>

Step 5: Install Required Libraries

pip install flask pyserial

Save dependencies:

pip freeze > requirements.txt

6. Project Structure

Height_Measurement/
│
├── venv/
│
├── app.py
│
└── requirements.txt

The complete website, including HTML, CSS and JavaScript, will be included inside app.py.

7. Create the Python Application

Create a file named app.py.

Important: Set SENSOR_HEIGHT_CM according to the actual height of your mounted sensor.

For this example, the sensor is mounted 200 cm above the floor.

from flask import Flask, jsonify, render_template_string
import serial
import threading
import time

app = Flask(__name__)

# ==================================
# CONFIGURATION
# ==================================

SERIAL_PORT = "COM3"
BAUD_RATE = 9600

# Sensor height from floor in centimeters
SENSOR_HEIGHT_CM = 200

# Measurement variables
distance = 0
person_height = 0

connection_status = "Disconnected"
last_updated = "--"


# ==================================
# ARDUINO SERIAL COMMUNICATION
# ==================================

def read_arduino():

    global distance, person_height
    global connection_status, last_updated

    while True:

        try:

            print("Connecting to Arduino...")

            arduino = serial.Serial(
                SERIAL_PORT,
                BAUD_RATE,
                timeout=2
            )

            time.sleep(2)

            connection_status = "Connected"

            print("Arduino Connected!")

            while True:

                line = arduino.readline().decode(
                    "utf-8",
                    errors="ignore"
                ).strip()

                if not line or line == "ERROR":
                    continue

                try:

                    measured_distance = float(line)

                    # Validate sensor measurement
                    if not 2 <= measured_distance < SENSOR_HEIGHT_CM:
                        continue

                    # Calculate person's height
                    calculated_height = (
                        SENSOR_HEIGHT_CM - measured_distance
                    )

                    distance = round(measured_distance, 2)

                    person_height = round(
                        calculated_height, 2
                    )

                    last_updated = time.strftime("%H:%M:%S")

                    print(
                        f"Distance: {distance} cm | "
                        f"Height: {person_height} cm"
                    )

                except ValueError:
                    continue

        except Exception as error:

            connection_status = "Disconnected"

            print("Arduino Error:", error)

            time.sleep(3)


# ==================================
# WEB DASHBOARD
# ==================================

HTML_PAGE = """






    Height Measurement System

    

    





    

        📏 Height Measurement System

        Arduino-Based Smart Height Monitoring

    


    

        

            

                🧍

                Person's Height

                

                    -- cm

                

                Calculated Height

            


            

                📡

                Sensor Distance

                

                    -- cm

                

                Distance from Sensor to Head

            

        


        

            Sensor Mounting Height

            -- cm

        


        

            

                Arduino Status:

                

                    Checking...

                

            

            

                Last Updated:

                --

            

        

    


    

        Arduino UNO + HC-SR04 | Python Flask

    


    





"""


# ==================================
# FLASK ROUTES
# ==================================

@app.route("/")
def home():

    return render_template_string(HTML_PAGE)


@app.route("/data")
def get_data():

    return jsonify({

        "height": person_height,

        "distance": distance,

        "mounting_height": SENSOR_HEIGHT_CM,

        "status": connection_status,

        "updated": last_updated

    })


# ==================================
# START APPLICATION
# ==================================

if __name__ == "__main__":

    thread = threading.Thread(
        target=read_arduino,
        daemon=True
    )

    thread.start()

    app.run(
        host="127.0.0.1",
        port=5000,
        debug=False
    )

8. Configure Sensor Height and COM Port

Open app.py and change these values:

SERIAL_PORT = "COM3"

SENSOR_HEIGHT_CM = 200

For example, if the sensor is mounted 210 cm above the floor:

SENSOR_HEIGHT_CM = 210

If Arduino is connected to COM5:

SERIAL_PORT = "COM5"

Remember: The mounting height is measured from the ultrasonic sensor's front measuring surface, not from the Arduino board or mounting bracket.

9. Run the Application

Connect Arduino UNO to your computer.
Upload the Arduino program.
Close Arduino IDE Serial Monitor.
Activate the Python virtual environment.
Run the application:

python app.py

Open the browser:

http://127.0.0.1:5000

Example Result

Suppose:

Sensor mounting height = 200 cm
Measured distance = 30 cm

Then:

[ H=200-30=170\text{ cm} ]

The dashboard will display:

Measurement	Value
Person's Height	170 cm
Sensor Distance	30 cm
Sensor Mounting Height	200 cm
Arduino Status	Connected

10. Troubleshooting

Problem	Solution
COM port error	Check Arduino COM port
Access denied	Close Arduino Serial Monitor
Arduino disconnected	Check USB connection
Height shows zero	Check sensor wiring and mounting height
Unstable readings	Keep the sensor fixed and person stationary
Incorrect height	Re-measure the sensor-to-floor distance
No sensor reading	Check TRIG and ECHO connections

11. Important Accuracy and Safety Notes

Mount the sensor securely and vertically.
Ensure the sensor has a clear view of the person's head.
Ask the person to stand straight and remain still.
Avoid measuring near walls or other objects that can reflect ultrasonic waves.
Take several measurements and use an average for better stability.
HC-SR04 readings can vary depending on the surface, angle and environment.
This is an educational prototype, not a medical-grade height measurement instrument.

12. Future Improvements

Students can extend this project with:

Automatic averaging of multiple readings.
Display height in both centimeters and feet/inches.
Save measurements in an SQLite database.
Add student name and measurement history.
Generate height measurement reports.
Add an LCD display.
Develop a school-based student height monitoring system.

Project Conclusion: This project demonstrates how an ultrasonic sensor, Arduino, Python serial communication and Flask web development can be combined to create a practical height measurement system.

Arduino DHT11 Temperature & Humidity Monitoring System

Ankit Chapagain — Tue, 03 Nov 2026 16:56:50 GMT

1. Project Overview

This project uses an Arduino UNO and DHT11 sensor to measure temperature and humidity and display the readings on a live web dashboard using Python Flask.

Technologies Used

Arduino UNO
DHT11 Temperature and Humidity Sensor
Arduino IDE
Python
Flask
PySerial
HTML, CSS and JavaScript

System Architecture

DHT11 Sensor
     |
     v
Arduino UNO
     |
     v
USB Serial Communication
     |
     v
Python Flask Application
     |
     v
Web Dashboard
     |
     v
Live Temperature & Humidity

2. Hardware Requirements

Component	Quantity
Arduino UNO	1
DHT11 Sensor	1
Jumper Wires	3
USB Cable	1
Computer/Laptop	1

DHT11 Connections

DHT11 Pin	Arduino UNO
VCC	5V
DATA	Digital Pin 2
GND	GND

For a bare four-pin DHT11 sensor, check its pinout and use the required pull-up resistor. Three-pin modules often include this resistor.

3. Arduino IDE Setup

Step 1: Install Arduino IDE

Download Arduino IDE:

https://www.arduino.cc/en/software

Install and open Arduino IDE.

Step 2: Install DHT11 Library

Open Arduino IDE.
Navigate to Sketch → Include Library → Manage Libraries.
Search for DHT sensor library.
Install DHT sensor library by Adafruit.
Install Adafruit Unified Sensor if requested.

Step 3: Arduino Code

Create a new Arduino sketch and upload the following code.

#include 

// Sensor configuration
#define DHTPIN 2
#define DHTTYPE DHT11

DHT dht(DHTPIN, DHTTYPE);

void setup() {

    // Start serial communication
    Serial.begin(9600);

    // Initialize DHT11
    dht.begin();
}

void loop() {

    // Read sensor values
    float temperature = dht.readTemperature();
    float humidity = dht.readHumidity();

    // Check sensor readings
    if (isnan(temperature) || isnan(humidity)) {

        Serial.println("ERROR");

    }
    else {

        // Send data to Python
        Serial.print(temperature);
        Serial.print(",");
        Serial.println(humidity);

    }

    delay(2000);
}

Expected Serial Output

28.00,65.00
29.00,64.00
30.00,63.00

The first value represents temperature in Celsius, and the second represents humidity in percentage.

4. Python Environment Setup

Step 1: Install Python

Download Python from:

https://www.python.org/downloads/

During installation, select Add Python to PATH.

Verify installation:

python --version

Step 2: Create Project Folder

Open PowerShell or Command Prompt.

mkdir DHT11_Website
cd DHT11_Website

Step 3: Create Python Virtual Environment

A virtual environment keeps project dependencies separate from other Python projects.

python -m venv venv

Step 4: Activate Virtual Environment

Windows PowerShell:

.\venv\Scripts\Activate.ps1

If PowerShell blocks activation, run:

Set-ExecutionPolicy -Scope Process -ExecutionPolicy Bypass

Then activate again:

.\venv\Scripts\Activate.ps1

Windows Command Prompt:

venv\Scripts\activate.bat

After successful activation, you should see:

(venv) C:\...\DHT11_Website>

Step 5: Install Required Libraries

pip install flask pyserial

Verify installed packages:

pip list

Step 6: Save Dependencies

pip freeze > requirements.txt

5. Project Structure

The project will contain one Python application file.

DHT11_Website/
│
├── venv/
│
├── app.py
│
└── requirements.txt

The HTML, CSS and JavaScript code will be included inside app.py, so a separate HTML file is not required.

6. Create the Python Application

Create a file named app.py.

Copy the following complete code:

from flask import Flask, jsonify, render_template_string
import serial
import threading
import time

app = Flask(__name__)

# Arduino Configuration
SERIAL_PORT = "COM3"
BAUD_RATE = 9600

# Sensor Variables
temperature = 0
humidity = 0

connection_status = "Disconnected"
last_updated = "--"


# =====================================
# ARDUINO SERIAL COMMUNICATION
# =====================================

def read_arduino():

    global temperature, humidity
    global connection_status, last_updated

    while True:

        try:

            print("Connecting to Arduino...")

            arduino = serial.Serial(
                SERIAL_PORT,
                BAUD_RATE,
                timeout=2
            )

            time.sleep(2)

            connection_status = "Connected"

            print("Arduino Connected!")

            while True:

                line = arduino.readline().decode(
                    "utf-8",
                    errors="ignore"
                ).strip()

                if not line or line == "ERROR":
                    continue

                try:

                    values = line.split(",")

                    if len(values) == 2:

                        temp = float(values[0])
                        hum = float(values[1])

                        temperature = temp
                        humidity = hum

                        last_updated = time.strftime("%H:%M:%S")

                        print(
                            f"Temperature: {temp} C | "
                            f"Humidity: {hum} %"
                        )

                except ValueError:

                    continue

        except Exception as error:

            connection_status = "Disconnected"

            print("Arduino Error:", error)

            time.sleep(3)


# =====================================
# HTML DASHBOARD
# =====================================

HTML_PAGE = """






    DHT11 Monitoring System

    

    





    

        🌡️ DHT11 Monitoring System

        Live Temperature and Humidity Dashboard

    


    

        

            

                🌡️

                Temperature

                

                    -- °C

                

                Room Temperature

            


            

                💧

                Humidity

                

                    -- %

                

                Air Humidity

            

        


        

            

                Arduino Status:

                

                    Checking...

                

            

            

                Last Updated:

                --

            

        

    


    

        Arduino UNO + DHT11 | Python Flask IoT Dashboard

    


    





"""


# =====================================
# FLASK ROUTES
# =====================================

@app.route("/")
def home():

    return render_template_string(HTML_PAGE)


@app.route("/data")
def get_data():

    return jsonify({

        "temperature": temperature,

        "humidity": humidity,

        "status": connection_status,

        "updated": last_updated

    })


# =====================================
# START APPLICATION
# =====================================

if __name__ == "__main__":

    thread = threading.Thread(
        target=read_arduino,
        daemon=True
    )

    thread.start()

    app.run(
        host="127.0.0.1",
        port=5000,
        debug=False
    )

7. Configure Arduino COM Port

Before running the application, identify the Arduino COM port.

Open Arduino IDE.
Connect Arduino UNO.
Select Tools → Port.
Note the COM port number.

For example:

SERIAL_PORT = "COM3"

If your Arduino uses COM5, change it to:

SERIAL_PORT = "COM5"

Important: Close Arduino IDE Serial Monitor before running the Python application because both applications cannot normally access the same serial port simultaneously.

8. Run the Application

Make sure your virtual environment is activated.

python app.py

Expected terminal output:

Connecting to Arduino...
Arduino Connected!

Temperature: 28.0 C | Humidity: 65.0 %
Temperature: 29.0 C | Humidity: 64.0 %

Running on http://127.0.0.1:5000

Open your web browser:

http://127.0.0.1:5000

Your live dashboard will display the temperature, humidity and Arduino connection status.

9. Troubleshooting

Problem	Possible Solution
COM port error	Check the correct Arduino COM port
Access denied	Close Arduino Serial Monitor
Arduino disconnected	Check USB cable and connection
No sensor readings	Check DHT11 wiring and library installation
Website not opening	Check whether Flask is running on port 5000
Python module not found	Activate virtual environment and install dependencies

10. Useful Commands

Task	Command
Create virtual environment	`python -m venv venv`
Activate environment	`venv\Scripts\activate`
Install Flask	`pip install flask`
Install PySerial	`pip install pyserial`
Save dependencies	`pip freeze > requirements.txt`
Run application	`python app.py`
Deactivate environment	`deactivate`

11. Future Improvements

After completing the basic project, students can extend it with:

Live temperature and humidity graphs.
Historical sensor data storage using SQLite.
Download sensor readings as CSV.
Temperature threshold alerts.
Multiple sensor monitoring.
Professional IoT dashboard design.
Remote access through a suitable network deployment.

Project Conclusion: This project demonstrates how Arduino hardware, sensor technology, serial communication and Python web development can be integrated to create a simple real-time IoT monitoring system.

Arduino Height Measurement System

Ankit Chapagain — Tue, 03 Nov 2026 16:53:38 GMT

1. Project Overview

The Arduino-based Height Measurement System uses an ultrasonic sensor to measure the distance between the sensor and a person's head.

The sensor is mounted at a fixed height, facing downward. When a person stands beneath it, the system measures the distance from the sensor to the person's head.

Python calculates the person's height using the following formula:

Person's Height = Sensor Mounting Height − Measured Distance

Technologies Used

Arduino UNO
HC-SR04 Ultrasonic Sensor
Arduino IDE
Python
Flask
PySerial
HTML, CSS and JavaScript

System Architecture

       HC-SR04 Sensor
              |
              v
          Arduino UNO
              |
              v
     USB Serial Communication
              |
              v
       Python Flask Server
              |
              v
       Height Calculation
              |
              v
        Web Dashboard
              |
              v
       Display Height (cm)

2. Hardware Requirements

Component	Quantity
Arduino UNO	1
HC-SR04 Ultrasonic Sensor	1
Jumper Wires	4
USB Cable	1
Computer/Laptop	1
Fixed mounting frame	1

3. Hardware Connections

HC-SR04 to Arduino UNO

HC-SR04 Pin	Arduino UNO
VCC	5V
GND	GND
TRIG	Digital Pin 9
ECHO	Digital Pin 10

Sensor Installation:

Mount the ultrasonic sensor horizontally at a fixed height.
The sensor must face vertically downward.
Keep the sensor stable.
The person should stand directly below the sensor.
Measure the distance from the sensor's ultrasonic face to the floor.

For example:

       HC-SR04 SENSOR
       (Fixed Position)
       ┌─────────────┐
       │             │
       └─────────────┘
              |
              |
              |  Measured Distance
              |
           _______
          /       \
         |  HEAD   |
         |         |
         | PERSON  |
         |         |
         |         |
         |         |
         |_________|

       ----------------
             FLOOR

Example:

Sensor mounting height = 200 cm
Distance from sensor to head = 30 cm

Person's height:

[ H=200-30 ]

[ \boxed{H=170\text{ cm}} ]

Important: The sensor mounting height must be measured accurately from the sensor's measuring face to the floor.

4. Arduino IDE Setup

Step 1: Install Arduino IDE

Download Arduino IDE:

https://www.arduino.cc/en/software

Install and open Arduino IDE.

Step 2: Arduino Code

The following program measures the distance using the HC-SR04 sensor and sends the measurement to Python through serial communication.

No additional Arduino library is required.

// HC-SR04 Configuration

#define TRIG_PIN 9
#define ECHO_PIN 10

void setup() {

    // Start serial communication
    Serial.begin(9600);

    // Configure sensor pins
    pinMode(TRIG_PIN, OUTPUT);
    pinMode(ECHO_PIN, INPUT);
}

void loop() {

    // Send ultrasonic trigger pulse
    digitalWrite(TRIG_PIN, LOW);
    delayMicroseconds(2);

    digitalWrite(TRIG_PIN, HIGH);
    delayMicroseconds(10);

    digitalWrite(TRIG_PIN, LOW);

    // Read echo duration
    long duration = pulseIn(ECHO_PIN, HIGH, 30000);

    if (duration == 0) {

        Serial.println("ERROR");

    }
    else {

        // Calculate distance in centimeters
        float distance = duration * 0.0343 / 2;

        // Send distance to Python
        Serial.println(distance);
    }

    delay(500);
}

Step 3: Upload the Program

Connect Arduino UNO to your computer.
Select the correct board: Arduino UNO.
Select the correct COM port.
Upload the program.
Check the Serial Monitor at 9600 baud.

Expected output:

These values represent the measured distance between the sensor and the person's head.

5. Python Environment Setup

Step 1: Install Python

Download Python:

https://www.python.org/downloads/

Verify installation:

python --version

Step 2: Create Project Folder

Open PowerShell or Command Prompt.

mkdir Height_Measurement
cd Height_Measurement

Step 3: Create Python Virtual Environment

python -m venv venv

Step 4: Activate Virtual Environment

Windows PowerShell:

.\venv\Scripts\Activate.ps1

If PowerShell blocks activation:

Set-ExecutionPolicy -Scope Process -ExecutionPolicy Bypass

Then activate again:

.\venv\Scripts\Activate.ps1

Windows Command Prompt:

venv\Scripts\activate.bat

After activation, you should see:

(venv) C:\...\Height_Measurement>

Step 5: Install Required Libraries

pip install flask pyserial

Save dependencies:

pip freeze > requirements.txt

6. Project Structure

Height_Measurement/
│
├── venv/
│
├── app.py
│
└── requirements.txt

The complete website, including HTML, CSS and JavaScript, will be included inside app.py.

7. Create the Python Application

Create a file named app.py.

Important: Set SENSOR_HEIGHT_CM according to the actual height of your mounted sensor.

For this example, the sensor is mounted 200 cm above the floor.

from flask import Flask, jsonify, render_template_string
import serial
import threading
import time

app = Flask(__name__)

# ==================================
# CONFIGURATION
# ==================================

SERIAL_PORT = "COM3"
BAUD_RATE = 9600

# Sensor height from floor in centimeters
SENSOR_HEIGHT_CM = 200

# Measurement variables
distance = 0
person_height = 0

connection_status = "Disconnected"
last_updated = "--"


# ==================================
# ARDUINO SERIAL COMMUNICATION
# ==================================

def read_arduino():

    global distance, person_height
    global connection_status, last_updated

    while True:

        try:

            print("Connecting to Arduino...")

            arduino = serial.Serial(
                SERIAL_PORT,
                BAUD_RATE,
                timeout=2
            )

            time.sleep(2)

            connection_status = "Connected"

            print("Arduino Connected!")

            while True:

                line = arduino.readline().decode(
                    "utf-8",
                    errors="ignore"
                ).strip()

                if not line or line == "ERROR":
                    continue

                try:

                    measured_distance = float(line)

                    # Validate sensor measurement
                    if not 2 <= measured_distance < SENSOR_HEIGHT_CM:
                        continue

                    # Calculate person's height
                    calculated_height = (
                        SENSOR_HEIGHT_CM - measured_distance
                    )

                    distance = round(measured_distance, 2)

                    person_height = round(
                        calculated_height, 2
                    )

                    last_updated = time.strftime("%H:%M:%S")

                    print(
                        f"Distance: {distance} cm | "
                        f"Height: {person_height} cm"
                    )

                except ValueError:
                    continue

        except Exception as error:

            connection_status = "Disconnected"

            print("Arduino Error:", error)

            time.sleep(3)


# ==================================
# WEB DASHBOARD
# ==================================

HTML_PAGE = """






    Height Measurement System

    

    





    

        📏 Height Measurement System

        Arduino-Based Smart Height Monitoring

    


    

        

            

                🧍

                Person's Height

                

                    -- cm

                

                Calculated Height

            


            

                📡

                Sensor Distance

                

                    -- cm

                

                Distance from Sensor to Head

            

        


        

            Sensor Mounting Height

            -- cm

        


        

            

                Arduino Status:

                

                    Checking...

                

            

            

                Last Updated:

                --

            

        

    


    

        Arduino UNO + HC-SR04 | Python Flask

    


    





"""


# ==================================
# FLASK ROUTES
# ==================================

@app.route("/")
def home():

    return render_template_string(HTML_PAGE)


@app.route("/data")
def get_data():

    return jsonify({

        "height": person_height,

        "distance": distance,

        "mounting_height": SENSOR_HEIGHT_CM,

        "status": connection_status,

        "updated": last_updated

    })


# ==================================
# START APPLICATION
# ==================================

if __name__ == "__main__":

    thread = threading.Thread(
        target=read_arduino,
        daemon=True
    )

    thread.start()

Django Workshop Day 2

Ankit Chapagain — Fri, 19 Jun 2026 04:53:53 GMT

Building a Simple Blog Website

What We Will Learn Today

Creating Django Apps
Understanding Views
URL Routing
Templates
render()
Sending Data to Templates
Loops
Conditions
Building a Simple Blog Website

11. What is a Django App?

Think of a project as a school.

Inside the school there are many departments.

Example:

School Website

├── Student App
├── Teacher App
├── Attendance App
├── Blog App

Each part is called an App.

Today we will create a Blog App.

Create app:

python manage.py startapp blog

Django creates:

blog/

├── admin.py
├── apps.py
├── models.py
├── views.py
├── tests.py
└── migrations/

For now we only need:

views.py

12. Understanding Views

A View is a Python function.

A View decides what the user sees.

Example:

from django.http import HttpResponse

def home(request):
    return HttpResponse("Welcome to my Blog")

When a user visits a page, Django calls a View.

Simple Flow:

User
 ↓
URL
 ↓
View
 ↓
Response

13. Creating Multiple Views

Open:

blog/views.py

Write:

from django.http import HttpResponse

def home(request):
    return HttpResponse("Home Page")

def about(request):
    return HttpResponse("About Page")

def contact(request):
    return HttpResponse("Contact Page")

Now we have three pages.

14. URL Routing

URL routing tells Django:

"When a user visits this URL, call this View."

Create:

blog/urls.py

Write:

from django.urls import path
from .views import *

urlpatterns = [

    path('', home),

    path('about/', about),

    path('contact/', contact),

]

Meaning:

/          → home()

/about/    → about()

/contact/  → contact()

15. Connect App URLs

Open:

project/urls.py

Write:

from django.contrib import admin
from django.urls import path,include

urlpatterns = [

    path('admin/', admin.site.urls),

    path('', include('blog.urls')),

]

Now Django can access our app URLs.

Flow:

Project URL
      ↓
Blog URL
      ↓
View

16. Why Templates?

Suppose we write:

return HttpResponse("Home Page")

This works.

But imagine a website with:

500 lines of HTML
CSS
Images
Navigation Bar

Writing everything inside Python becomes difficult.

So Django uses Templates.

Template = HTML File

17. Creating Templates Folder

Create:

blog/

└── templates/

    └── blog/

        ├── home.html

        ├── about.html

        └── contact.html

18. Creating Home Page

home.html






    Home




    My Blog Website

    Welcome to Django Workshop

19. Using render()

Open views.py

from django.shortcuts import render

def home(request):

    return render(
        request,
        "blog/home.html"
    )

What happens?

User opens URL
       ↓
View executes
       ↓
render() finds home.html
       ↓
Browser shows page

20. Sending Data to HTML

Instead of hard coding text:

Welcome Ram

We can send data from Python.

View:

def home(request):

    context = {

        "name":"Ram"

    }

    return render(
        request,
        "blog/home.html",
        context
    )

HTML:

Welcome {{ name }}

Output:

Welcome Ram

21. Sending Multiple Data

View:

context = {

    "name":"Ram",

    "course":"Django",

    "day":2

}

HTML:

{{ name }}

{{ course }}

Day {{ day }}

Output:

Ram

Django

Day 2

22. Loops in Templates

Suppose we have students.

View:

context = {

    "students":[

        "Ram",

        "Sita",

        "Hari",

        "Gita"

    ]

}

HTML:

Student List

{% for student in students %}

    {{ student }}

{% endfor %}

Output:

Ram

Sita

Hari

Gita

The loop works exactly like Python.

23. Conditions in Templates

HTML:

{% if students %}

    Students Available

{% else %}

    No Students Available

{% endif %}

Django checks the condition and displays the result.

24. Mini Project - Simple Blog Website

Now let's build a complete Blog Website.

Instead of using a database, we will store blogs inside a Python list.

This keeps things simple.

Step 1: Create Blog Data

views.py

from django.shortcuts import render

blogs = [

    {
        "title":"Python Basics",
        "author":"Ram"
    },

    {
        "title":"Django Introduction",
        "author":"Sita"
    },

    {
        "title":"HTML Fundamentals",
        "author":"Hari"
    }

]

Step 2: Send Data to Template

def home(request):

    context = {

        "blogs":blogs

    }

    return render(
        request,
        "blog/home.html",
        context
    )

Step 3: Display Blogs

home.html






    Blog Website




My Blog Website

{% for blog in blogs %}

    {{ blog.title }}

    Author : {{ blog.author }}

    

{% endfor %}

Output:

My Blog Website

Python Basics
Author : Ram

Django Introduction
Author : Sita

HTML Fundamentals
Author : Hari

Step 4: Add About Page

views.py

def about(request):

    return render(
        request,
        "blog/about.html"
    )

about.html

About Us


This website was created using Django.

Step 5: Add Navigation

home.html

Home

About

about.html

Home

About

Now users can move between pages.

Final Project Structure

project/

├── manage.py

├── blog/

│   ├── views.py

│   ├── urls.py

│   └── templates/

│       └── blog/

│           ├── home.html

│           └── about.html

Day 2 Summary

Today we learned:

Django Apps
Views
URLs
Templates
render()
Context
Variables
Loops
Conditions
Creating Multiple Pages
Building a Simple Blog Website

Complete Flow:

User
 ↓
URL
 ↓
View
 ↓
Context Data
 ↓
Template
 ↓
Browser

Tomorrow (Day 3) we will connect our Blog Website to a real database using Models and Admin Panel.

Day 1 Django Note

Ankit Chapagain — Thu, 18 Jun 2026 10:55:12 GMT

1. What is Django?

Django is a Python framework used to build websites and web applications.

It gives us a proper structure to build web apps easily.

With Django, we can build:

Blog website
School system
Inventory system
E-commerce website
Learning platform
Admin dashboard

Django mainly helps us with:

URL handling
Views
HTML rendering
Database structure
Security

2. How Django Works

Django works in a simple flow:

User opens a URL
        ↓
Django checks urls.py
        ↓
Django calls a view function
        ↓
View returns response or HTML page
        ↓
User sees output in browser

Simple example:

User opens /
        ↓
urls.py finds matching path
        ↓
home view is called
        ↓
home.html is rendered

3. Django MVT Architecture

Django follows MVT architecture.

M = Model
V = View
T = Template

Simple meaning:

Component	Purpose
Model	Database structure
View	Python logic
Template	HTML page

For now, just understand:

URL calls View
View renders Template
Model is used to design database table

4. Create Project Folder

mkdir django_day_1
cd django_day_1

5. Create Virtual Environment

python -m venv venv

Activate virtual environment.

Windows

venv\Scripts\activate

Mac/Linux

source venv/bin/activate

6. Install Django

pip install django

Check version:

django-admin --version

7. Create Django Project

django-admin startproject myproject

Go inside project:

cd myproject

Run server:

python manage.py runserver

Open in browser:

http://127.0.0.1:8000/

You should see Django's default welcome page.

8. Important Files

Project structure:

myproject/
│
├── manage.py
│
└── myproject/
    ├── settings.py
    ├── urls.py
    ├── asgi.py
    └── wsgi.py

manage.py

Used to run Django commands.

Example:

python manage.py runserver

settings.py

Contains project settings such as:

Installed apps
Database settings
Template settings
Middleware

urls.py

Connects URL with view function.

9. First Page Using HttpResponse

Open:

myproject/urls.py

Write:

from django.contrib import admin
from django.urls import path
from django.http import HttpResponse

def home(request):
    return HttpResponse("Welcome to Django Day 1")

urlpatterns = [
    path("admin/", admin.site.urls),
    path("", home),
]

Open:

http://127.0.0.1:8000/

Output:

Welcome to Django Day 1

10. What is HttpResponse?

HttpResponse sends a direct response from Django to the browser.

Example:

return HttpResponse("Hello Django")

We can also send simple HTML:

return HttpResponse("Hello Django")

But for real pages, we use HTML templates.

Day 2 at Python

Ankit Chapagain — Wed, 17 Jun 2026 01:44:10 GMT

Topics Covered

1. List Slicing
2. Tuple
3. Dictionary
4. Set
5. Exception Handling
6. Different Types of Exceptions
7. File Handling
8. Login System Using File Handling and Exception Handling

1. List Slicing

In Day 2, we learned about lists.

A list is used to store multiple values in one variable.

Example:

fruits = ["apple", "banana", "mango", "orange", "grapes"]

Now, we will learn list slicing.

List slicing means taking a specific part of a list.

List Index Revision

In Python, list index starts from 0.

Example:

fruits = ["apple", "banana", "mango", "orange"]

Index values:

apple   -> index 0
banana  -> index 1
mango   -> index 2
orange  -> index 3

Example:

fruits = ["apple", "banana", "mango", "orange"]

print(fruits[0])
print(fruits[1])

Output:

apple
banana

Basic List Slicing

Example:

numbers = [10, 20, 30, 40, 50]

print(numbers[0:3])

Output:

[10, 20, 30]

Explanation:

numbers[0:3]

means start from index 0 and stop before index 3.

It includes:

numbers[0]
numbers[1]
numbers[2]

It does not include index 3.

More List Slicing Examples

numbers = [10, 20, 30, 40, 50, 60]

print(numbers[0:3])
print(numbers[2:5])
print(numbers[:4])
print(numbers[3:])

Output:

[10, 20, 30]
[30, 40, 50]
[10, 20, 30, 40]
[40, 50, 60]

Explanation:

numbers[0:3]

starts from index 0 and stops before index 3.

numbers[2:5]

starts from index 2 and stops before index 5.

numbers[:4]

starts from the beginning and stops before index 4.

numbers[3:]

starts from index 3 and goes until the end.

Negative Indexing

Python also supports negative indexing.

Example:

fruits = ["apple", "banana", "mango", "orange"]

print(fruits[-1])
print(fruits[-2])

Output:

orange
mango

Explanation:

-1

means last item.

-2

means second last item.

Negative Slicing

Example:

numbers = [10, 20, 30, 40, 50, 60]

print(numbers[-3:])

Output:

[40, 50, 60]

Explanation:

numbers[-3:]

means take the last three items.

Slicing With Step

Example:

numbers = [10, 20, 30, 40, 50, 60]

print(numbers[0:6:2])

Output:

[10, 30, 50]

Explanation:

numbers[0:6:2]

means:

Start from index 0
Stop before index 6
Move by step 2

Reverse a List Using Slicing

Example:

numbers = [10, 20, 30, 40, 50]

print(numbers[::-1])

Output:

[50, 40, 30, 20, 10]

Explanation:

[::-1]

is used to reverse a list.

List Slicing Questions

Question 1

Print the first three items from a list.

Solution:

fruits = ["apple", "banana", "mango", "orange", "grapes"]

print(fruits[0:3])

Output:

['apple', 'banana', 'mango']

Question 2

Print the last two items from a list.

Solution:

fruits = ["apple", "banana", "mango", "orange", "grapes"]

print(fruits[-2:])

Output:

['orange', 'grapes']

Question 3

Reverse a list using slicing.

Solution:

numbers = [1, 2, 3, 4, 5]

print(numbers[::-1])

Output:

[5, 4, 3, 2, 1]

2. Tuple

A tuple is used to store multiple values in one variable.

It is similar to a list.

But the main difference is:

List is changeable.
Tuple is not changeable.

That means after creating a tuple, we cannot directly add, remove, or change its items.

Example:

fruits = ("apple", "banana", "mango")

print(fruits)

Output:

('apple', 'banana', 'mango')

Here, fruits is a tuple.

Accessing Tuple Items

Tuple index also starts from 0, just like list.

Example:

fruits = ("apple", "banana", "mango")

print(fruits[0])
print(fruits[1])
print(fruits[2])

Output:

apple
banana
mango

Explanation:

fruits[0]

gives "apple".

fruits[1]

gives "banana".

fruits[2]

gives "mango".

Tuple Cannot Be Changed

Example:

fruits = ("apple", "banana", "mango")

fruits[0] = "orange"

print(fruits)

This gives an error.

Because tuple does not allow item change.

Why Use Tuple?

We use tuple when we want to store values that should not change.

Example:

days = ("Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday")

Days of the week are fixed, so tuple is a good choice.

Another example:

location = (26.4525, 87.2718)

This can store latitude and longitude.

Looping Through Tuple

Example:

fruits = ("apple", "banana", "mango")

for fruit in fruits:
    print(fruit)

Output:

apple
banana
mango

Explanation:

Tuple is iterable.

So we can use a for loop to read each item one by one.

Tuple Question 1

Write a program to store five student names in a tuple and print them one by one.

Solution:

students = ("Ram", "Sita", "Hari", "Gita", "Shyam")

for student in students:
    print(student)

Output:

Ram
Sita
Hari
Gita
Shyam

Tuple Question 2

Write a program to find the length of a tuple.

Solution:

numbers = (10, 20, 30, 40, 50)

print("Total items:", len(numbers))

Output:

Total items: 5

Explanation:

len() counts how many items are inside the tuple.

Tuple Question 3

Write a program to check whether "apple" exists in a tuple or not.

Solution:

fruits = ("apple", "banana", "mango")

if "apple" in fruits:
    print("Apple exists")
else:
    print("Apple does not exist")

Output:

Apple exists

3. Dictionary

A dictionary is used to store data in key-value pairs.

Example:

student = {
    "name": "Ram",
    "age": 18,
    "address": "Kathmandu"
}

print(student)

Output:

{'name': 'Ram', 'age': 18, 'address': 'Kathmandu'}

Here:

"name"

is a key.

"Ram"

is the value.

Real-Life Example of Dictionary

A student has different details:

Name: Ram
Age: 18
Address: Kathmandu

In Python, we can store this like:

student = {
    "name": "Ram",
    "age": 18,
    "address": "Kathmandu"
}

Dictionary is useful when we want to store related information.

Accessing Dictionary Values

Example:

student = {
    "name": "Ram",
    "age": 18,
    "address": "Kathmandu"
}

print(student["name"])
print(student["age"])
print(student["address"])

Output:

Ram
18
Kathmandu

Explanation:

We use the key to access the value.

student["name"]

gives "Ram".

Updating Dictionary Value

Example:

student = {
    "name": "Ram",
    "age": 18
}

student["age"] = 19

print(student)

Output:

{'name': 'Ram', 'age': 19}

Explanation:

The value of "age" was changed from 18 to 19.

Adding New Key-Value Pair

Example:

student = {
    "name": "Ram",
    "age": 18
}

student["address"] = "Kathmandu"

print(student)

Output:

{'name': 'Ram', 'age': 18, 'address': 'Kathmandu'}

Explanation:

A new key "address" was added to the dictionary.

Removing Item from Dictionary

Example:

student = {
    "name": "Ram",
    "age": 18,
    "address": "Kathmandu"
}

student.pop("age")

print(student)

Output:

{'name': 'Ram', 'address': 'Kathmandu'}

Explanation:

pop() removes the item with the given key.

Looping Through Dictionary

Example:

student = {
    "name": "Ram",
    "age": 18,
    "address": "Kathmandu"
}

for key in student:
    print(key)

Output:

name
age
address

This prints only keys.

To print values:

student = {
    "name": "Ram",
    "age": 18,
    "address": "Kathmandu"
}

for key in student:
    print(student[key])

Output:

Ram
18
Kathmandu

To print both key and value:

student = {
    "name": "Ram",
    "age": 18,
    "address": "Kathmandu"
}

for key, value in student.items():
    print(key, ":", value)

Output:

name : Ram
age : 18
address : Kathmandu

Dictionary Question 1

Write a program to store student name, age, and address in a dictionary and print them.

Solution:

student = {
    "name": "Sita",
    "age": 19,
    "address": "Pokhara"
}

print("Name:", student["name"])
print("Age:", student["age"])
print("Address:", student["address"])

Output:

Name: Sita
Age: 19
Address: Pokhara

Dictionary Question 2

Write a program to store product name, price, and quantity. Then calculate total price.

Solution:

product = {
    "name": "Pen",
    "price": 20,
    "quantity": 5
}

total = product["price"] * product["quantity"]

print("Product:", product["name"])
print("Total price:", total)

Output:

Product: Pen
Total price: 100

Explanation:

Price is 20.

Quantity is 5.

So:

20 * 5 = 100

Dictionary Question 3

Write a program to update a student's marks.

Solution:

student = {
    "name": "Ram",
    "marks": 75
}

student["marks"] = 85

print(student)

Output:

{'name': 'Ram', 'marks': 85}

4. Set

A set is used to store multiple values in one variable.

But set has two important features:

1. Set does not allow duplicate values.
2. Set does not maintain fixed order.

Example:

numbers = {10, 20, 30, 40}

print(numbers)

Output may be:

{40, 10, 20, 30}

The order may be different.

That is normal in set.

Set Does Not Allow Duplicate Values

Example:

numbers = {10, 20, 20, 30, 30, 40}

print(numbers)

Output:

{40, 10, 20, 30}

Explanation:

Duplicate values are automatically removed.

Adding Item to Set

Example:

fruits = {"apple", "banana"}

fruits.add("mango")

print(fruits)

Output may be:

{'apple', 'banana', 'mango'}

The order may be different.

Removing Item from Set

Example:

fruits = {"apple", "banana", "mango"}

fruits.remove("banana")

print(fruits)

Output:

{'apple', 'mango'}

Looping Through Set

Example:

fruits = {"apple", "banana", "mango"}

for fruit in fruits:
    print(fruit)

Output may be:

banana
apple
mango

Explanation:

Set is iterable.

But the order is not fixed.

Why Use Set?

Set is useful when we want unique values only.

Example:

students = {"Ram", "Sita", "Ram", "Hari", "Sita"}

print(students)

Output:

{'Ram', 'Sita', 'Hari'}

Duplicate names are removed.

Set Question 1

Write a program to remove duplicate numbers from a list.

Solution:

numbers = [10, 20, 20, 30, 30, 40]

unique_numbers = set(numbers)

print(unique_numbers)

Output:

{40, 10, 20, 30}

Explanation:

The list contains duplicate values.

When we convert it into a set, duplicate values are removed.

Set Question 2

Write a program to add a new student name in a set.

Solution:

students = {"Ram", "Sita", "Hari"}

students.add("Gita")

print(students)

Output may be:

{'Ram', 'Sita', 'Hari', 'Gita'}

Set Question 3

Write a program to check whether "Ram" exists in a set or not.

Solution:

students = {"Ram", "Sita", "Hari"}

if "Ram" in students:
    print("Ram exists")
else:
    print("Ram does not exist")

Output:

Ram exists

5. Exception Handling

Exception handling means handling errors in a program.

Sometimes our program may get an error while running.

Example:

a = int(input("Enter first number: "))
b = int(input("Enter second number: "))

print(a / b)

If the user enters:

10
0

Then the program gives an error because division by zero is not allowed.

To handle this kind of error, we use:

try
except

Basic Try Except

Example:

try:
    a = int(input("Enter first number: "))
    b = int(input("Enter second number: "))

    result = a / b

    print("Result:", result)

except:
    print("Something went wrong")

Explanation:

The code that may cause an error is written inside try.

If an error happens, the code inside except runs.

So instead of crashing, the program shows a message.

Better Try Except

It is better to mention the exact error name.

Example:

try:
    a = int(input("Enter first number: "))
    b = int(input("Enter second number: "))

    result = a / b

    print("Result:", result)

except ZeroDivisionError:
    print("Cannot divide by zero")

except ValueError:
    print("Please enter numbers only")

Explanation:

ZeroDivisionError happens when we divide by zero.

ValueError happens when we enter invalid number input.

6. Different Types of Exceptions

Python has many types of exceptions.

Some common exceptions are:

1. ValueError
2. ZeroDivisionError
3. FileNotFoundError
4. IndexError
5. KeyError
6. TypeError
7. NameError
8. PermissionError

1. ValueError

ValueError happens when the value is not valid.

Example:

age = int("hello")

This gives an error because "hello" cannot be converted into an integer.

Correct handling:

try:
    age = int(input("Enter your age: "))
    print("Your age is", age)

except ValueError:
    print("Please enter a valid number")

2. ZeroDivisionError

ZeroDivisionError happens when we divide a number by zero.

Example:

try:
    a = 10
    b = 0

    result = a / b

    print(result)

except ZeroDivisionError:
    print("Cannot divide by zero")

Output:

Cannot divide by zero

3. FileNotFoundError

FileNotFoundError happens when we try to read a file that does not exist.

Example:

try:
    with open("data.txt", "r") as file:
        data = file.read()
        print(data)

except FileNotFoundError:
    print("File not found")

4. IndexError

IndexError happens when we try to access an index that does not exist in a list.

Example:

try:
    numbers = [10, 20, 30]

    print(numbers[5])

except IndexError:
    print("Index does not exist")

Output:

Index does not exist

Explanation:

The list has only three items.

Available indexes are:

0, 1, 2

But we tried to access index 5.

So IndexError happened.

5. KeyError

KeyError happens when we try to access a dictionary key that does not exist.

Example:

try:
    student = {
        "name": "Ram",
        "age": 18
    }

    print(student["address"])

except KeyError:
    print("Key does not exist")

Output:

Key does not exist

Explanation:

The dictionary has only:

name
age

But we tried to access:

address

So KeyError happened.

6. TypeError

TypeError happens when we perform an operation with the wrong data type.

Example:

try:
    result = "Age: " + 20
    print(result)

except TypeError:
    print("Cannot add string and number directly")

Output:

Cannot add string and number directly

Correct way:

result = "Age: " + str(20)
print(result)

7. NameError

NameError happens when we use a variable that has not been created.

Example:

try:
    print(username)

except NameError:
    print("Variable is not defined")

Output:

Variable is not defined

8. PermissionError

PermissionError happens when Python does not have permission to read or write a file.

Example:

try:
    with open("/root/data.txt", "w") as file:
        file.write("Hello")

except PermissionError:
    print("You do not have permission to write this file")

Handling Multiple Exceptions Together

Example:

try:
    a = int(input("Enter first number: "))
    b = int(input("Enter second number: "))

    result = a / b

    print("Result:", result)

except ValueError:
    print("Please enter numbers only")

except ZeroDivisionError:
    print("Cannot divide by zero")

except Exception as e:
    print("Something went wrong:", e)

Explanation:

ValueError handles invalid input.

ZeroDivisionError handles division by zero.

Exception handles any other unexpected error.

Try Except Else

else runs only when there is no error.

Example:

try:
    age = int(input("Enter your age: "))

except ValueError:
    print("Please enter a valid number")

else:
    print("Your age is", age)

Explanation:

If the user enters a correct number, else runs.

If the user enters text like "abc", except runs.

Try Except Finally

finally always runs.

Example:

try:
    number = int(input("Enter a number: "))
    print(number)

except ValueError:
    print("Invalid input")

finally:
    print("Program finished")

Explanation:

Whether error happens or not, finally runs.

7. File Handling

File handling means working with files using Python.

Using file handling, we can:

1. Create a file
2. Write data into a file
3. Read data from a file
4. Add new data into an existing file

Opening a File

Python uses open() to open a file.

Syntax:

file = open("filename.txt", "mode")

Common file modes:

"r"  read mode
"w"  write mode
"a"  append mode

Write Mode

Write mode is used to write data into a file.

Example:

file = open("student.txt", "w")

file.write("Hello, this is my first file.")

file.close()

Explanation:

student.txt is the file name.

"w" means write mode.

write() writes data into the file.

close() closes the file.

Important:

If the file does not exist, Python creates it.

If the file already exists, write mode replaces old content.

Reading a File

Example:

file = open("student.txt", "r")

data = file.read()

print(data)

file.close()

Output:

Hello, this is my first file.

Explanation:

"r" means read mode.

read() reads the file content.

Append Mode

Append mode is used to add new data without deleting old data.

Example:

file = open("student.txt", "a")

file.write("\nThis is new line.")

file.close()

Explanation:

"a" means append mode.

It adds new content at the end of the file.

\n means new line.

Better Way: Using with open()

The better way to work with files is:

with open("student.txt", "w") as file:
    file.write("Hello Python")

Here, we do not need to write:

file.close()

Python automatically closes the file.

Read File Using with open()

Example:

with open("student.txt", "r") as file:
    data = file.read()
    print(data)

File Handling With Exception Handling

File handling and exception handling are often used together.

Why?

Because file errors can happen.

For example:

1. File may not exist.
2. User may enter wrong input.
3. Program may not have permission to read/write file.

Example:

try:
    with open("student.txt", "r") as file:
        data = file.read()
        print(data)

except FileNotFoundError:
    print("File does not exist")

Explanation:

If student.txt exists, Python reads the file.

If it does not exist, FileNotFoundError happens.

Then except block runs.

8. File-Based Login System

Now we will create a simple login system using file handling.

In this system:

Each user will have their own file.
The username will be used as the file name.
The password will be saved inside that file.

Example:

If username is:

ram

Then Python creates:

ram.txt

Inside ram.txt, the password is saved.

Full Login System Code

def register():
    username = input("Enter your username: ")
    password = input("Enter your password: ")

    try:
        file = open(f"{username}.txt", "r")
        print("Username already exists")
        file.close()

    except FileNotFoundError:
        with open(f"{username}.txt", "w") as f:
            f.write(password)

        print("User registered successfully")

    except Exception as e:
        print("Something went wrong while registering:", e)


def login():
    username = input("Enter your username: ")
    password = input("Enter your password: ")

    try:
        file = open(f"{username}.txt", "r")
        file.close()

    except FileNotFoundError:
        print("User not found")
        return

    except Exception as e:
        print("Something went wrong while opening user file:", e)
        return

    try:
        with open(f"{username}.txt", "r") as f:
            checkpass = f.readline()

            if password == checkpass:
                print("Welcome")
            else:
                print("Sorry, incorrect password")

    except Exception as e:
        print("Something went wrong while checking password:", e)


def ask():
    x = input("Do you want to register or login? Press r for register and l for login: ")

    if x == "r":
        register()

    elif x == "l":
        login()

    else:
        print("Invalid choice")


ask()

9. Explanation of Login System

Register Function

def register():

This function is used to register a new user.

username = input("Enter your username: ")
password = input("Enter your password: ")

Here, the program asks the user to enter username and password.

Checking If Username Already Exists

try:
    file = open(f"{username}.txt", "r")
    print("Username already exists")
    file.close()

Here, the program tries to open a file with the username.

Example:

If username is:

ram

Then it tries to open:

ram.txt

If the file exists, it means the username is already registered.

So the program prints:

Username already exists

Creating File for New User

except FileNotFoundError:
    with open(f"{username}.txt", "w") as f:
        f.write(password)

    print("User registered successfully")

If the file does not exist, Python gives FileNotFoundError.

That means the username is new.

So the program creates a new file and saves the password inside it.

Example:

If username is:

sita

Then file name becomes:

sita.txt

And inside that file, the password is saved.

Login Function

def login():

This function is used to login an existing user.

username = input("Enter your username: ")
password = input("Enter your password: ")

The program asks for username and password.

Checking If User Exists

try:
    file = open(f"{username}.txt", "r")
    file.close()

The program tries to open the user's file.

If the file exists, the user exists.

User Not Found

except FileNotFoundError:
    print("User not found")
    return

If the file does not exist, the program prints:

User not found

Here, return is used to stop the function.

This is better than exit() because exit() closes the whole program immediately.

Reading Saved Password

with open(f"{username}.txt", "r") as f:
    checkpass = f.readline()

This opens the user's file and reads the saved password.

The saved password is stored in:

checkpass

Checking Password

if password == checkpass:
    print("Welcome")
else:
    print("Sorry, incorrect password")

If entered password and saved password are same, login is successful.

Otherwise, it prints incorrect password.

10. Simpler Version Like Your Original Code

This is very close to your original code.

def register():
    username = input("Enter your username: ")
    password = input("Enter your password: ")

    try:
        file = open(f"{username}.txt", "r")
        print("Username already exists")
        file.close()

    except:
        with open(f"{username}.txt", "w") as f:
            f.write(password)

        print("User registered successfully")


def login():
    username = input("Enter your username: ")
    password = input("Enter your password: ")

    try:
        file = open(f"{username}.txt", "r")
        file.close()

    except:
        print("User not found")
        return

    with open(f"{username}.txt", "r") as f:
        checkpass = f.readline()

        if password == checkpass:
            print("Welcome")
        else:
            print("Sorry, incorrect password")


def ask():
    x = input("Do you want to register or login? Press r for register and l for login: ")

    if x == "r":
        register()
    else:
        login()


ask()

This version is okay for beginners.

But for better practice, this is preferred:

except FileNotFoundError:

instead of only:

except:

Because except: catches all errors, but FileNotFoundError catches only file-not-found error.

11. Important Note About This Login System

This login system is only for learning.

It teaches:

1. Function
2. Input
3. File handling
4. Try and except
5. User already exists
6. User not found
7. Password checking

But in real websites or real applications, passwords should not be saved directly like this.

In real projects, passwords should be hashed before saving.

For now, this is good for beginner-level Python file handling practice.

12. Class Explanation Flow

You can explain the login system like this:

When registering:
Python checks if username.txt exists.
If it exists, the user already exists.
If it does not exist, Python creates the file and saves the password.

When logging in:
Python checks if username.txt exists.
If it does not exist, user not found.
If it exists, Python reads the saved password.
Then it compares the saved password with the entered password.

13. Day 3 Practice Questions

List Slicing Questions

Create a list of 10 numbers and print the first 5 numbers.
Print the last 3 numbers from a list.
Reverse a list using slicing.
Print every second item from a list.

Tuple Questions

Create a tuple of five fruits and print each fruit.
Create a tuple of numbers and find its length.
Check whether "Python" exists in a tuple.
Try to change a tuple item and observe the error.

Dictionary Questions

Create a dictionary for a student with name, age, class, and address.
Create a dictionary for a product and calculate total price.
Update the marks of a student in a dictionary.
Print all keys and values from a dictionary.

Set Questions

Create a set of numbers with duplicate values and print it.
Add a new item to a set.
Remove an item from a set.
Convert a list with duplicate values into a set.

Exception Handling Questions

Take two numbers and divide them. Handle ZeroDivisionError.
Take age from user. Handle ValueError.
Try to access an invalid list index. Handle IndexError.
Try to access an invalid dictionary key. Handle KeyError.
Try to read a file that does not exist. Handle FileNotFoundError.

File Handling Questions

Create a file named message.txt and write "Hello Python" into it.
Read and print the content of message.txt.
Append three student names into students.txt.
Read a file and handle FileNotFoundError.

Final Project Question

Create a login system using file handling.

Requirements:

1. Register user.
2. Login user.
3. If user already exists, show message.
4. If user does not exist, show user not found.
5. If password is correct, show welcome.
6. If password is wrong, show incorrect password.
7. Use try and except.
8. Store each user password in username.txt file.

14. Day 3 Final Summary

Today we learned:

List slicing:
Used to get part of a list.

Tuple:
Used to store multiple values that should not change.

Dictionary:
Used to store data in key-value pairs.

Set:
Used to store unique values.

Exception handling:
Used to handle errors without crashing the program.

File handling:
Used to create, read, write, and append files.

Login system:
Used file handling and exception handling together.

Final simple memory:

List      -> changeable collection
Tuple     -> unchangeable collection
Dictionary -> key-value collection
Set       -> unique value collection
try-except -> error handling
File      -> permanent data storage

Second Day At Workshop Python

Ankit Chapagain — Tue, 16 Jun 2026 06:11:20 GMT

After installing Python and setting up the virtual environment, the first program we usually write is:

print("Hello, World!")

1. Variables

A variable is a name used to store data in a program.

When we write a program, we need to store different values like name, age, marks, price, address, total amount, and so on. For that, we use variables.

Example:

name = "Ram"
age = 18

Here, name is a variable that stores "Ram".

age is a variable that stores 18.

We can print the values stored in variables using print().

Example:

name = "Ram"
age = 18

print(name)
print(age)

Output:

Ram
18

In Python, we do not need to write the data type manually. Python automatically understands the type of value.

For example:

name = "Sita"
age = 20

Python understands that "Sita" is text and 20 is a number.

A variable name should be meaningful.

Good variable names:

student_name = "Ram"
total_marks = 450
product_price = 500

Bad variable names:

a = "Ram"
x = 450
p = 500

These are not wrong, but they are not clear. Good variable names help us understand the program easily.

Question:

Write a program to store student name, age, and address. Then print all details.

Solution:

name = "Sita"
age = 19
address = "Pokhara"

print("Name:", name)
print("Age:", age)
print("Address:", address)

Output:

Name: Sita
Age: 19
Address: Pokhara

Explanation:

Here, we created three variables.

name stores the student name.

age stores the student age.

address stores the student address.

Then we used print() to display all values.

2. Data Types

Data type means the type of value stored in a variable.

Different types of data are used in programming. Some values are numbers, some are text, some are decimal numbers, and some are true or false values.

Common data types in Python are:

int means integer or whole number.

Example:

age = 20

float means decimal number.

Example:

price = 99.5

str means string or text.

Example:

name = "Ram"

bool means boolean value. It can be either True or False.

Example:

is_student = True

list means collection of multiple values.

Example:

marks = [80, 90, 85]

We can check the data type of any variable using type().

Example:

age = 20
price = 99.5
name = "Ram"
is_student = True
marks = [80, 90, 85]

print(type(age))
print(type(price))
print(type(name))
print(type(is_student))
print(type(marks))

Output:

Question:

Write a program to create variables of different data types and print their types.

Solution:

name = "Hari"
age = 21
height = 5.7
passed = True
numbers = [10, 20, 30]

print(type(name))
print(type(age))
print(type(height))
print(type(passed))
print(type(numbers))

Output:

Explanation:

"Hari" is text, so its type is str.

21 is a whole number, so its type is int.

5.7 is a decimal number, so its type is float.

True is a boolean value, so its type is bool.

[10, 20, 30] is a list, so its type is list.

3. Input

Input means taking data from the user.

In real programs, values are not always fixed. Sometimes we need to ask the user to enter data.

For example, in a billing system, the user may enter product name, quantity, and price.

In Python, we use input() to take input from the user.

Example:

name = input("Enter your name: ")

print("Hello", name)

Output:

Enter your name: Ram
Hello Ram

Here, the program asks the user to enter a name. The entered value is stored in the variable name.

Important point:

input() always takes value as a string.

Example:

age = input("Enter your age: ")

print(type(age))

If the user enters 20, Python still treats it as string.

Output:

That is why we need type casting when we want to perform mathematical calculations.

Question:

Write a program to take name and city from the user and print them.

Solution:

name = input("Enter your name: ")
city = input("Enter your city: ")

print("Your name is", name)
print("You live in", city)

Example Output:

Enter your name: Ram
Enter your city: Kathmandu
Your name is Ram
You live in Kathmandu

Explanation:

The first input() takes the user's name.

The second input() takes the user's city.

Then both values are printed using print().

4. Type Casting

Type casting means converting one data type into another data type.

Sometimes data comes in one type, but we need it in another type.

For example, input() gives value as string. But if we want to add two numbers, we must convert them into integer or float.

Common type casting functions are:

int() converts value into integer.

float() converts value into decimal number.

str() converts value into string.

Example:

num = "10"
num = int(num)

print(num)
print(type(num))

Output:

Here, "10" was a string. After using int(), it became an integer.

Why type casting is needed:

a = input("Enter first number: ")
b = input("Enter second number: ")

print(a + b)

If user enters 10 and 20, output will be:

This happens because both values are strings. Python joins strings using +.

Correct way:

a = int(input("Enter first number: "))
b = int(input("Enter second number: "))

print(a + b)

Output:

Question:

Write a program to take two numbers from the user and print their sum.

Solution:

a = int(input("Enter first number: "))
b = int(input("Enter second number: "))

total = a + b

print("Total is", total)

Example Output:

Enter first number: 10
Enter second number: 20
Total is 30

Explanation:

input() takes values from the user.

int() converts those values into numbers.

Then + adds the numbers.

Without int(), Python would join the values as strings.

5. Operators

Operators are symbols used to perform operations.

For example:

a = 10
b = 5

print(a + b)

Here, + is an operator.

It adds two numbers.

Common arithmetic operators are:

+ is used for addition.

- is used for subtraction.

* is used for multiplication.

/ is used for division.

// is used for floor division.

% is used to find remainder.

** is used for power.

Example:

a = 10
b = 3

print(a + b)
print(a - b)
print(a * b)
print(a / b)
print(a // b)
print(a % b)
print(a ** b)

Output:

13
7
30
3.3333333333333335
3
1
1000

Explanation:

10 + 3 gives 13.

10 - 3 gives 7.

10 * 3 gives 30.

10 / 3 gives decimal division result.

10 // 3 gives only the whole number part.

10 % 3 gives the remainder.

10 ** 3 means 10 to the power 3.

Question:

Write a program to take two numbers and perform addition, subtraction, multiplication, and division.

Solution:

a = int(input("Enter first number: "))
b = int(input("Enter second number: "))

print("Addition:", a + b)
print("Subtraction:", a - b)
print("Multiplication:", a * b)
print("Division:", a / b)

Example Output:

Enter first number: 20
Enter second number: 5
Addition: 25
Subtraction: 15
Multiplication: 100
Division: 4.0

Explanation:

The program takes two numbers from the user.

Then it uses different operators to perform calculations.

+ adds the values.

- subtracts the values.

* multiplies the values.

/ divides the values.

6. Conditional Statement

Conditional statement is used to make decisions in a program.

Sometimes we want to run code only when a condition is true.

For example:

If age is greater than or equal to 18, the person can vote.

Otherwise, the person cannot vote.

Example:

age = 18

if age >= 18:
    print("You can vote")
else:
    print("You cannot vote")

Output:

You can vote

Here, Python checks the condition:

age >= 18

If the condition is true, the code inside if runs.

If the condition is false, the code inside else runs.

Example with marks:

marks = 75

if marks >= 40:
    print("Pass")
else:
    print("Fail")

Output:

Pass

Question:

Write a program to check whether a number is even or odd.

Solution:

num = int(input("Enter a number: "))

if num % 2 == 0:
    print("Even number")
else:
    print("Odd number")

Example Output:

Enter a number: 7
Odd number

Explanation:

The % operator gives the remainder.

If a number is divided by 2 and the remainder is 0, the number is even.

For example:

8 % 2

gives 0, so 8 is even.

But:

7 % 2

gives 1, so 7 is odd.

7. For Loop

A for loop is used to repeat code.

When we want to do the same work again and again, we use loops.

Example:

for i in range(5):
    print(i)

Output:

Here, range(5) gives numbers from 0 to 4.

The loop runs one time for each number.

First time, i is 0.

Second time, i is 1.

Third time, i is 2.

This continues until 4.

Example:

for i in range(1, 6):
    print(i)

Output:

Here, range(1, 6) starts from 1 and stops before 6.

So it prints 1 to 5.

Example with step:

for i in range(1, 10, 2):
    print(i)

Output:

Here:

1 is the starting value.

10 is the stopping value, but it is not included.

2 is the step value.

Question:

Write a program to print numbers from 1 to 10 using for loop.

Solution:

for i in range(1, 11):
    print(i)

Output:

Explanation:

range(1, 11) starts from 1.

It stops before 11.

So the loop prints numbers from 1 to 10.

Each value is stored in i one by one and printed.

8. Iterable

An iterable is something that we can loop through.

In simple words, iterable means a value that gives items one by one.

Examples of iterables are:

String

List

Range

Tuple

Dictionary

A string is iterable because we can get each letter one by one.

Example:

name = "Ram"

for letter in name:
    print(letter)

Output:

R
a
m

Here, Python reads the string letter by letter.

A list is also iterable.

Example:

fruits = ["apple", "banana", "mango"]

for fruit in fruits:
    print(fruit)

Output:

apple
banana
mango

Here, Python reads the list item by item.

So, when we use a for loop, we mostly loop through an iterable.

Question:

Write a program to print each letter of the word Python.

Solution:

word = "Python"

for letter in word:
    print(letter)

Output:

P
y
t
h
o
n

Explanation:

The word "Python" is a string.

A string is iterable.

So the for loop takes one letter at a time and prints it.

9. List

A list is used to store multiple values in one variable.

Example:

fruits = ["apple", "banana", "mango"]

Here, fruits is a list.

It stores three values.

Lists are useful when we have many related values.

Example:

marks = [80, 90, 75, 85]

Instead of creating many variables like this:

mark1 = 80
mark2 = 90
mark3 = 75
mark4 = 85

We can store all marks in one list.

marks = [80, 90, 75, 85]

Accessing list items:

List index starts from 0.

Example:

fruits = ["apple", "banana", "mango"]

print(fruits[0])
print(fruits[1])
print(fruits[2])

Output:

apple
banana
mango

Here:

fruits[0] gives "apple".

fruits[1] gives "banana".

fruits[2] gives "mango".

Adding item to list:

fruits = ["apple", "banana"]

fruits.append("mango")

print(fruits)

Output:

['apple', 'banana', 'mango']

append() adds a new item at the end of the list.

Removing item from list:

fruits = ["apple", "banana", "mango"]

fruits.remove("banana")

print(fruits)

Output:

['apple', 'mango']

remove() removes the given item from the list.

Looping through list:

fruits = ["apple", "banana", "mango"]

for fruit in fruits:
    print(fruit)

Output:

apple
banana
mango

Question:

Write a program to find total marks from a list.

Solution:

marks = [80, 90, 75, 85]

total = 0

for mark in marks:
    total = total + mark

print("Total marks:", total)

Output:

Total marks: 330

Explanation:

marks is a list.

At first, total is 0.

The for loop takes each mark from the list.

First, 80 is added to total.

Then, 90 is added.

Then, 75 is added.

Then, 85 is added.

Finally, the total becomes 330.

10. Function

A function is a reusable block of code.

When we write the same code again and again, our program becomes long and difficult to manage.

To solve this problem, we use functions.

A function is created using def.

Example:

def greet():
    print("Hello")

greet()

Output:

Hello

Explanation:

def is used to define a function.

greet is the function name.

The code inside the function runs only when we call the function.

Here:

greet()

calls the function.

Why do we use functions?

We use functions to avoid repeating code.

We use functions to make code clean.

We use functions to divide a big program into small parts.

We use functions to reuse code many times.

Function with parameter:

A parameter is a value received by a function.

Example:

def greet(name):
    print("Hello", name)

greet("Ram")
greet("Sita")

Output:

Hello Ram
Hello Sita

Explanation:

Here, name is a parameter.

When we call the function, we send a value.

In greet("Ram"), "Ram" is sent to the function.

So the function prints:

Hello Ram

Function with return:

return sends value back from the function.

Example:

def add(a, b):
    return a + b

result = add(10, 20)

print(result)

Output:

Explanation:

The function receives two numbers.

It adds them.

Then it returns the answer.

The returned answer is stored in result.

Difference between print and return:

print() only displays the value.

return sends the value back so we can use it later.

Example:

def add(a, b):
    return a + b

answer = add(10, 20)

final = answer + 50

print(final)

Output:

Here, the returned value is used again in another calculation.

Function Question 1:

Create a function to add two numbers.

Solution:

def add(a, b):
    total = a + b
    return total

answer = add(10, 20)

print("Sum is", answer)

Output:

Sum is 30

Explanation:

The function name is add.

It receives two values: a and b.

Inside the function, both values are added.

The result is returned using return.

Then the returned value is stored in answer.

Function Question 2:

Create a function to check whether a number is even or odd.

Solution:

def check_even_odd(num):
    if num % 2 == 0:
        return "Even"
    else:
        return "Odd"

number = int(input("Enter a number: "))

result = check_even_odd(number)

print(result)

Example Output:

Enter a number: 8
Even

Explanation:

The function receives a number.

Inside the function, we check:

num % 2 == 0

If the remainder is 0, the number is even.

Otherwise, the number is odd.

The function returns "Even" or "Odd".

Function Question 3:

Create a function to find total marks from a list.

Solution:

def calculate_total(marks):
    total = 0

    for mark in marks:
        total = total + mark

    return total

student_marks = [80, 90, 75, 85]

answer = calculate_total(student_marks)

print("Total marks:", answer)

Output:

Total marks: 330

Explanation:

The function receives a list of marks.

At first, total is 0.

The for loop goes through each mark.

Each mark is added to total.

Finally, the function returns the total marks.

Function Question 4:

Create a function to find the largest number from a list.

Solution:

def find_largest(numbers):
    largest = numbers[0]

    for number in numbers:
        if number > largest:
            largest = number

    return largest

numbers = [10, 25, 7, 90, 45]

answer = find_largest(numbers)

print("Largest number is", answer)

Output:

Largest number is 90

Explanation:

The function receives a list of numbers.

At first, we assume the first number is the largest.

largest = numbers[0]

Then the for loop checks each number.

If any number is greater than the current largest number, we update the largest value.

At the end, the function returns the largest number.

Tricky Function Question:

What will be the output of this program?

def add_item(item, items=[]):
    items.append(item)
    return items

print(add_item("apple"))
print(add_item("banana"))
print(add_item("mango"))

Output:

['apple']
['apple', 'banana']
['apple', 'banana', 'mango']

Explanation:

This is tricky because the default list items=[] is created only once.

It is not created again every time the function is called.

So every function call uses the same list.

First call:

add_item("apple")

The list becomes:

['apple']

Second call:

add_item("banana")

The same list becomes:

['apple', 'banana']

Third call:

add_item("mango")

The same list becomes:

['apple', 'banana', 'mango']

Correct way:

def add_item(item, items=None):
    if items is None:
        itexuu

    items.append(item)
    return items

print(add_item("apple"))
print(add_item("banana"))
print(add_item("mango"))

Output:

['apple']
['banana']
['mango']

Explanation:

Here, we used None instead of an empty list.

Every time the function is called without a list, a new empty list is created.

So old values are not reused.

Day 5 topics

Ankit Chapagain — Sun, 24 May 2026 02:20:48 GMT

a name

1\. Quick revision of Python and OOP
2. Very simple database concept
3. Creating table and selecting data using SQLite
4. Linux terminal commands
5. Basic Vim commands
6. Git introduction
7. GitHub introduction
8. Git staging area
9. Git commit and snapshot
10. Basic Git workflow practice

Part 1: Quick Python Revision

Until now, we learned:

Variables
Data types
Conditionals
Loops
Functions
File handling
Exception handling
Dictionaries
OOP basics

In Python, we can store student data like this:

student = {
    "name": "Ram",
    "age": 18,
    "marks": 80
}

This works while the program is running.

But after the program is closed, this data is lost.

So we need a database.

Part 2: Little Bit of Database

What is a database?

A database is a place where we store data permanently in an organized way.

Example:

A school may store:

Student name
Age
Class
Marks
Address
Phone number

A database stores data in tables.

What is a table?

A table is like a register.

Example:

id	name	age	marks
1	Ram	18	80
2	Sita	19	90

Here:

id, name, age, marks = columns
Ram and Sita data = rows

What is SQLite?

SQLite is a simple database.

It is good for beginners because:

It is simple.
It stores data in one file.
Python already supports it.
No extra installation is needed.

Example database file:

students.db

Part 3: Simple SQLite Code

For Day 5, we are not learning full CRUD.

We are only learning:

Create table
Insert simple data
Select/read data

Simple code

import sqlite3

connection = sqlite3.connect("students.db")
cursor = connection.cursor()

cursor.execute("""
CREATE TABLE IF NOT EXISTS students (
    id INTEGER PRIMARY KEY AUTOINCREMENT,
    name TEXT,
    age INTEGER,
    marks REAL
)
""")

cursor.execute("""
INSERT INTO students (name, age, marks)
VALUES ('Ram', 18, 80)
""")

cursor.execute("SELECT * FROM students")

students = cursor.fetchall()

for student in students:
    print(student)

connection.commit()
connection.close()

Explanation

import sqlite3

This imports the SQLite database module.

connection = sqlite3.connect("students.db")

This connects Python to the database.

If students.db does not exist, Python creates it.

cursor = connection.cursor()

Cursor is used to run SQL commands.

CREATE TABLE IF NOT EXISTS students

This creates a table named students.

SELECT * FROM students

This reads all data from the students table.

Part 4: Now Main Topic: Git and GitHub

Before learning Git, students should understand one problem.

Imagine you are building a Python project.

Day 1:

print("Hello")

Day 2:

You add a menu.

Day 3:

You add student management.

Day 4:

You add database.

Day 5:

Something breaks.

Now the problem is:

Which file changed?
When did it change?
What was working before?
Can we go back to old code?
How can multiple students work on the same project?

This is where Git helps.

Part 5: What is Git?

Git is a version control system.

Simple meaning:

Git tracks changes in our project.

It remembers the history of our code.

With Git, we can see:

What changed
When it changed
Who changed it
Why it changed
Previous versions of the project

Simple definition for students

Git is a tool that helps us save different versions of our project properly.

Instead of doing this:

project-final
project-final-new
project-final-latest
project-final-real
project-final-last

We use Git.

Git manages versions professionally.

Part 6: Why is Git Important?

Git is important because it helps us:

Track code changes
Save project history
Go back to old versions
Work safely on new features
Work in teams
Upload code to GitHub
Avoid losing code

Real-life example

Suppose you are working on a student management system.

Your project is working properly.

Then you try to add a database.

After adding the database, the project stops working.

Without Git:

You may not know what went wrong.
You may not know which file changed.
You may have to rewrite code again.

With Git:

You can check previous versions.
You can compare changes.
You can return to the working version.

Part 7: What is GitHub?

GitHub is a website/platform where we can store our Git projects online.

Simple meaning:

Git = tool on your computer
GitHub = website to store and share Git projects

Example:

Git tracks your project locally.
GitHub stores your project online.

Simple analogy

Git = camera
GitHub = online photo album

Git takes snapshots of your code.

GitHub stores those snapshots online.

Part 8: Git vs GitHub

Git	GitHub
Installed on your computer	Website/platform
Tracks code changes	Stores code online
Works locally	Works on the internet
Can be used without GitHub	Needs Git project
Tool	Hosting service

Simple line:

Git is the tool. GitHub is the place where we upload Git projects.

Part 9: Basic Linux Commands for Git

Before using Git, students should know basic terminal commands.

Check current folder

pwd

This shows where you are.

List files and folders

ls

Show hidden files also:

ls -a

Change folder

cd folder_name

Go back one folder:

cd ..

Go to home folder:

cd ~

Create folder

mkdir my_project

Create file

touch app.py

Clear terminal

clear

Remove file

rm app.py

Remove folder

rm -r my_project

Be careful with rm.

Show file content

cat app.py

Run Python file

python3 app.py

or:

python app.py

Part 10: Basic Vim Commands

Sometimes Git may open Vim.

For example, when writing commit messages.

Students do not need to master Vim now.

They only need basic survival commands.

Open file in Vim

vim app.py

Insert mode

Press:

Now you can write.

Save and exit

Press:

Esc

Then type:

:wq

Then press Enter.

Exit without saving

Press:

Esc

Then type:

:q!

Then press Enter.

Save only

Press:

Esc

Then type:

:w

Part 11: Git Installation Check

To check if Git is installed:

git --version

Example output:

git version 2.39.0

If this shows a version, Git is installed.

Part 12: Git Configuration

Before using Git, we should set name and email.

git config --global user.name "Your Name"
git config --global user.email "your@email.com"

Example:

git config --global user.name "Ram Sharma"
git config --global user.email "ram@gmail.com"

To check configuration:

git config --list

Part 13: What is a Git Repository?

A Git repository means a project folder where Git is tracking changes.

To create a Git repository:

git init

Example:

mkdir student_project
cd student_project
git init

Now Git starts tracking this project.

What happens after `git init`?

Git creates a hidden folder named:

.git

This .git folder stores Git history and information.

To see it:

ls -a

You will see:

.git

Important:

Do not delete the .git folder unless you want to remove Git tracking from the project.

Part 14: Git Workflow

Git has three main areas:

1\. Working Directory
2. Staging Area
3. Repository

This is very important.

1. Working Directory

This is your normal project folder.

This is where you create and edit files.

Example:

app.py
main.py
students.db
README.md

When you change a file, the change first stays in the working directory.

2. Staging Area

The staging area is a preparation area.

Before saving changes permanently in Git history, we first add them to staging.

Command:

git add app.py

or:

git add .

3. Repository

The repository is where Git permanently saves the committed history.

Command:

git commit -m "message"

Example:

git commit -m "Add student management code"

Part 15: What is Git Staging?

Staging means choosing which changes should go into the next commit.

Imagine you changed three files:

app.py
database.py
notes.txt

But you only want to save app.py and database.py in one commit.

You can do:

git add app.py
git add database.py
git commit -m "Add database feature"

Now notes.txt is not included in that commit.

So staging gives control.

Simple classroom analogy

Imagine you are packing a school bag.

On the table, you have:

Math book
Science book
Copy
Pen
Lunch box
Football

You do not put everything into the bag.

You choose only what is needed.

That choosing step is like staging.

Table = working directory
Selected items = staging area
Packed bag = commit

Part 16: What is a Git Commit?

A commit is a saved version of your project.

When we commit, Git saves the staged changes into history.

Command:

git commit -m "Initial commit"

The message should explain what changed.

Good commit messages:

Add student model
Create database table
Fix login error
Update README file

Bad commit messages:

done
final
changes
abc
test

Part 17: What is a Snapshot in Git?

A snapshot is a saved picture of your project at a specific time.

When you commit, Git creates a snapshot.

Example:

Commit 1: Initial project
Commit 2: Add student management
Commit 3: Add database connection
Commit 4: Fix marks calculation

Each commit is like a photo of your project.

If something breaks later, you can check old snapshots.

Simple analogy

Imagine taking photos while building a house.

Photo 1:

Empty land

Photo 2:

Foundation completed

Photo 3:

Walls completed

Photo 4:

Roof completed

Git commit is like taking these photos of your code.

Part 18: Important Git Commands

1. Initialize Git

git init

Starts Git tracking in a folder.

2. Check status

git status

Shows current condition of files.

It tells:

Untracked files
Modified files
Staged files
Clean working tree

3. Add file to staging

git add app.py

Add all changes:

git add .

4. Commit changes

git commit -m "Initial commit"

This saves staged changes into Git history.

5. View commit history

git log

Short version:

git log --oneline

6. See changes

git diff

This shows what changed before staging.

7. See staged changes

git diff --staged

This shows what is already staged.

Part 19: First Git Practice

Ask students to do this step by step.

Step 1: Create project folder

mkdir git_practice
cd git_practice

Step 2: Initialize Git

git init

Step 3: Create Python file

touch app.py

Step 4: Write Python code

Open file:

vim app.py

Press:

Write:

print("Hello Git")

Save and exit:

Esc
:wq

Step 5: Check status

git status

Git will show app.py as untracked.

Untracked means:

Git sees the file, but Git is not tracking it yet.

Step 6: Add to staging

git add app.py

Now check status again:

git status

Now the file is staged.

Step 7: Commit

git commit -m "Create first Python file"

Now Git has saved the first snapshot.

Step 8: Check history

git log --oneline

You will see your commit.

Part 20: Second Git Practice

Now edit app.py.

vim app.py

Change code to:

print("Hello Git")
print("This is my second line")

Save and exit.

Now check status:

git status

Git will show that app.py is modified.

See what changed

git diff

This shows the new line added.

Stage and commit again

git add app.py
git commit -m "Add second print message"

Now check history:

git log --oneline

You will see two commits.

Part 21: Understanding File States in Git

A file in Git can have different states.

1. Untracked

Git sees the file but is not tracking it.

Example:

touch notes.txt
git status

notes.txt will be untracked.

2. Modified

Git is already tracking the file, but you changed it.

Example:

vim app.py
git status

Now app.py may show as modified.

3. Staged

The file is ready to be committed.

Example:

git add app.py
git status

Now it is staged.

4. Committed

The file is saved in Git history.

Example:

git commit -m "Update app"

Now it is committed.

Part 22: Simple Git Flow Diagram

Working Directory
      |
      | git add
      v
Staging Area
      |
      | git commit
      v
Repository / Git History

Example:

Write code
↓
git status
↓
git add .
↓
git status
↓
git commit -m "message"
↓
git log --oneline

Part 23: What is GitHub Account?

GitHub is an online platform.

To use GitHub, students need:

GitHub account
Repository on GitHub
Git installed locally
Internet connection

GitHub helps us:

Upload projects
Share projects
Collaborate with team
Show portfolio
Submit assignments
Work with companies

Part 24: What is a Remote Repository?

A remote repository is a Git repository stored online.

Example:

Local repository = project on your laptop
Remote repository = project on GitHub

To connect local project with GitHub, we use:

git remote add origin repository_url

Example:

git remote add origin https://github.com/username/project-name.git

Part 25: Push and Pull

Push

Push means sending local commits to GitHub.

git push

Simple meaning:

Laptop to GitHub

Pull

Pull means bringing latest code from GitHub to your laptop.

git pull

Simple meaning:

GitHub to laptop

Clone

Clone means downloading a GitHub project to your laptop.

git clone repository_url

Example:

git clone https://github.com/username/project-name.git

Part 26: First GitHub Upload Practice

Step 1: Create a repository on GitHub

Go to GitHub and create a new repository.

Example name:

git-practice

Do not add README from GitHub for now.

Step 2: Connect local project to GitHub

Inside your local project folder:

git remote add origin https://github.com/username/git-practice.git

Step 3: Rename branch to main

git branch -M main

Step 4: Push code

git push -u origin main

Now the code is uploaded to GitHub.

Part 27: Common GitHub Upload Flow

After the first upload, the regular flow is:

git status
git add .
git commit -m "Your message"
git push

This is the most common Git workflow.

Students should memorize this flow.

Part 28: README File

A README.md file explains the project.

Create README:

touch README.md

Write:

# Student Management System

This is a simple Python project.

## Features

- Add student
- View student
- Learn Git and GitHub

Then:

git add README.md
git commit -m "Add README file"
git push

Part 29: What is `.gitignore`?

.gitignore tells Git which files not to track.

Example:

We may not want to track:

__pycache__
.env
database files
temporary files

Create .gitignore:

touch .gitignore

Example content:

__pycache__/
*.pyc
.env

Then commit it:

git add .gitignore
git commit -m "Add gitignore file"

Part 30: Important Git Terms

Repository

A Git-tracked project.

Commit

A saved version of the project.

Staging

Preparing selected changes for commit.

Snapshot

A saved picture of project state at a point in time.

Remote

Online Git repository, usually on GitHub.

Push

Send local commits to GitHub.

Pull

Bring latest changes from GitHub to local computer.

Clone

Download a GitHub repository.

Branch

A separate line of development.

Branches can be covered more deeply on Day 6.

Part 31: Common Mistakes Students Make

Mistake 1: Forgetting `git add`

Wrong:

git commit -m "Update code"

If files are not staged, commit may not include changes.

Correct:

git add .
git commit -m "Update code"

Mistake 2: Bad commit messages

Bad:

git commit -m "done"

Good:

git commit -m "Add student database table"

Mistake 3: Using GitHub without committing

Students may think code goes to GitHub automatically.

It does not.

Correct flow:

git add .
git commit -m "message"
git push

Mistake 4: Confusing Git and GitHub

Remember:

Git is local.
GitHub is online.

Part 32: Class Activity

Give students this task:

Task: Create and upload a simple Python project

Requirements

Create a folder:

student_git_project

Create a file:

app.py

Write:

print("Student Management System")

name = input("Enter student name: ")
age = input("Enter student age: ")

print("Name:", name)
print("Age:", age)

Then use Git:

git init
git status
git add app.py
git commit -m "Create student input program"

Create README.md:

# Student Git Project

This is a simple Python project for learning Git and GitHub.

Then:

git add README.md
git commit -m "Add README"

Finally upload to GitHub:

git remote add origin https://github.com/username/student_git_project.git
git branch -M main
git push -u origin main

Part 33: Teacher Explanation Script

You can explain like this:

"Until now, we wrote Python code and saved files normally. But in real projects, simply saving files is not enough. We need to track changes. We need to know what changed, when it changed, and how to go back if something breaks. Git helps us manage the history of our project. GitHub helps us store that project online and share it with others."

Then say:

"Git works in three steps. First, we write code in the working directory. Second, we stage the changes using git add. Third, we save the changes using git commit. A commit is like a snapshot of our project."

Part 34: Final Summary for Students

Today we learned:

Database stores data permanently.
SQLite is a simple database.
Git tracks code changes.
GitHub stores Git projects online.
Git and GitHub are different.
Git has working directory, staging area, and repository.
Staging means preparing changes before commit.
Commit means saving a snapshot.
Push means uploading to GitHub.
Pull means downloading latest changes from GitHub.
Clone means copying a GitHub project to local computer.

Day 5 Homework

Homework 1: Git practice

Create a new folder:

day5_homework

Create a Python file:

main.py

Write any simple Python program.

Then use:

git init
git add .
git commit -m "Initial homework commit"

Modify the file and commit again:

git add .
git commit -m "Update homework program"

Check history:

git log --oneline

Homework 2: GitHub practice

Upload the homework project to GitHub.

Commands:

git remote add origin your_repository_url
git branch -M main
git push -u origin main

Homework 3: Write answers

Students should write short answers:

1\. What is Git?
2. What is GitHub?
3. What is the difference between Git and GitHub?
4. What is staging?
5. What is a commit?
6. What is a snapshot?
7. What is push?
8. What is pull?
9. What is clone?
10. Why is Git important?

Best One-Line Explanation

Git helps us track project history, and GitHub helps us store and share that project online.

Day 4 Python Notes

Ankit Chapagain — Fri, 22 May 2026 15:10:19 GMT

Topic: Python with SQLite Database

Topics Covered

What is a Database?
What is SQLite?
Difference Between File Handling and Database
Basic SQL Commands
Python with SQLite
Create Table
Insert Data
Fetch Data
Update Data
Delete Data
Complete SQLite CRUD Program
Practice Questions
Day 4 Summary

1. What is a Database?

A database is used to store data in an organized way.

In Day 3, we stored data using files.

Example:

ram.txt
sita.txt
hari.txt

But file handling becomes difficult when we have lots of data.

Example:

If we want to store student details:

Name: Ram
Age: 18
Address: Kathmandu

Using files is possible, but searching, updating, and deleting data becomes hard.

So we use a database.

A database stores data in tables.

Example:

id	name	age	address
1	Ram	18	Kathmandu
2	Sita	19	Pokhara
3	Hari	20	Biratnagar

2. What is SQLite?

SQLite is a small and simple database.

It stores data inside a single file.

Example:

school.db

SQLite is good for learning because:

It is simple.
It does not need server setup.
It works directly with Python.
Python already has SQLite built in.

We do not need to install anything extra.

We only need to import:

import sqlite3

3. File Handling vs Database

File Handling

In file handling, we store data in text files.

Example:

ram.txt

Inside the file:

This is okay for small programs.

But it is not good for storing many users or many student records.

Database

In a database, data is stored in tables.

Example:

id	username	password
1	ram	12345
2	sita	abc123

Database makes it easier to:

Add data
View data
Search data
Update data
Delete data

These operations are called CRUD.

4. What is CRUD?

CRUD means:

Letter	Meaning	Example
C	Create	Add new student
R	Read	View students
U	Update	Edit student data
D	Delete	Remove student

In database:

CRUD	SQL Command
Create	`INSERT`
Read	`SELECT`
Update	`UPDATE`
Delete	`DELETE`

5. What is SQL?

SQL means Structured Query Language.

SQL is used to talk with the database.

We use SQL commands to create tables, insert data, read data, update data, and delete data.

Example:

SELECT * FROM students;

This means:

Show all data from the students table.

6. Basic SQL Commands

1. CREATE TABLE

Used to create a new table.

Example:

CREATE TABLE students (
    id INTEGER PRIMARY KEY AUTOINCREMENT,
    name TEXT,
    age INTEGER,
    address TEXT
);

Explanation:

id INTEGER PRIMARY KEY AUTOINCREMENT

This creates an ID that increases automatically.

name TEXT

This stores text data.

age INTEGER

This stores number data.

address TEXT

This stores text data.

2. INSERT

Used to add data into a table.

Example:

INSERT INTO students (name, age, address)
VALUES ('Ram', 18, 'Kathmandu');

This adds one student into the students table.

3. SELECT

Used to read data from a table.

Example:

SELECT * FROM students;

This shows all students.

Example:

SELECT name, age FROM students;

This shows only name and age.

4. WHERE

Used to filter data.

Example:

SELECT * FROM students
WHERE id = 1;

This shows only the student whose ID is 1.

5. UPDATE

Used to change existing data.

Example:

UPDATE students
SET age = 20
WHERE id = 1;

This changes the age of the student whose ID is 1.

Important:

Always use WHERE while updating.

Without WHERE, all rows may be updated.

6. DELETE

Used to remove data.

Example:

DELETE FROM students
WHERE id = 1;

This deletes the student whose ID is 1.

Important:

Always use WHERE while deleting.

Without WHERE, all data may be deleted.

7. Python with SQLite

To use SQLite in Python, we use:

import sqlite3

Basic structure:

import sqlite3

connection = sqlite3.connect("school.db")

cursor = connection.cursor()

cursor.execute("SQL command here")

connection.commit()

connection.close()

8. Meaning of Important Lines

`sqlite3.connect()`

connection = sqlite3.connect("school.db")

This connects Python to the SQLite database.

If school.db does not exist, Python creates it automatically.

`cursor`

cursor = connection.cursor()

A cursor is a helper that runs SQL commands.

Simple explanation:

Database is like a notebook.

Connection opens the notebook.

Cursor is like a pen that writes or reads inside the notebook.

`execute()`

cursor.execute("SELECT * FROM students")

This runs SQL commands.

`commit()`

connection.commit()

This saves changes.

We use commit() after:

Create table
Insert data
Update data
Delete data

For SELECT, commit is not necessary.

`close()`

connection.close()

This closes the database connection.

9. Create Table Using Python

import sqlite3

connection = sqlite3.connect("school.db")
cursor = connection.cursor()

cursor.execute("""
CREATE TABLE IF NOT EXISTS students (
    id INTEGER PRIMARY KEY AUTOINCREMENT,
    name TEXT NOT NULL,
    age INTEGER NOT NULL,
    address TEXT NOT NULL
)
""")

connection.commit()
connection.close()

print("Table created successfully")

Explanation:

CREATE TABLE IF NOT EXISTS students

This creates the students table only if it does not already exist.

10. Insert Data Using Python

import sqlite3

connection = sqlite3.connect("school.db")
cursor = connection.cursor()

cursor.execute("""
INSERT INTO students (name, age, address)
VALUES (?, ?, ?)
""", ("Ram", 18, "Kathmandu"))

connection.commit()
connection.close()

print("Student inserted successfully")

Explanation:

VALUES (?, ?, ?)

The question marks are placeholders.

The actual values are passed here:

("Ram", 18, "Kathmandu")

This is safer than writing values directly inside SQL.

11. Fetch Data Using Python

import sqlite3

connection = sqlite3.connect("school.db")
cursor = connection.cursor()

cursor.execute("SELECT * FROM students")

students = cursor.fetchall()

for student in students:
    print(student)

connection.close()

Output example:

(1, 'Ram', 18, 'Kathmandu')
(2, 'Sita', 19, 'Pokhara')

12. `fetchone()` vs `fetchall()`

`fetchone()`

Gets only one row.

student = cursor.fetchone()

Example output:

(1, 'Ram', 18, 'Kathmandu')

`fetchall()`

Gets all rows.

students = cursor.fetchall()

Example output:

[
    (1, 'Ram', 18, 'Kathmandu'),
    (2, 'Sita', 19, 'Pokhara')
]

13. Update Data Using Python

import sqlite3

connection = sqlite3.connect("school.db")
cursor = connection.cursor()

cursor.execute("""
UPDATE students
SET name = ?, age = ?, address = ?
WHERE id = ?
""", ("Ram Sharma", 20, "Biratnagar", 1))

connection.commit()
connection.close()

print("Student updated successfully")

Explanation:

This updates the student whose ID is 1.

14. Delete Data Using Python

import sqlite3

connection = sqlite3.connect("school.db")
cursor = connection.cursor()

cursor.execute("""
DELETE FROM students
WHERE id = ?
""", (1,))

connection.commit()
connection.close()

print("Student deleted successfully")

Important:

(1,)

This is a single-value tuple.

Do not write:

(1)

Because (1) is just a number, not a tuple.

15. Complete SQLite CRUD Program

Save the file as:

student_database.py

import sqlite3

def connect_db():
    connection = sqlite3.connect("school.db")
    return connection

def create_table():
    connection = connect_db()
    cursor = connection.cursor()

    cursor.execute("""
    CREATE TABLE IF NOT EXISTS students (
        id INTEGER PRIMARY KEY AUTOINCREMENT,
        name TEXT NOT NULL,
        age INTEGER NOT NULL,
        address TEXT NOT NULL
    )
    """)

    connection.commit()
    connection.close()

    print("Table created successfully")

def insert_student():
    name = input("Enter student name: ")
    age = int(input("Enter student age: "))
    address = input("Enter student address: ")

    connection = connect_db()
    cursor = connection.cursor()

    cursor.execute("""
    INSERT INTO students (name, age, address)
    VALUES (?, ?, ?)
    """, (name, age, address))

    connection.commit()
    connection.close()

    print("Student inserted successfully")

def view_students():
    connection = connect_db()
    cursor = connection.cursor()

    cursor.execute("SELECT * FROM students")

    students = cursor.fetchall()

    connection.close()

    if len(students) == 0:
        print("No students found")
    else:
        print("\n--- Student List ---")

        for student in students:
            print("ID:", student[0])
            print("Name:", student[1])
            print("Age:", student[2])
            print("Address:", student[3])
            print("--------------------")

def search_student():
    student_id = int(input("Enter student ID: "))

    connection = connect_db()
    cursor = connection.cursor()

    cursor.execute("""
    SELECT * FROM students
    WHERE id = ?
    """, (student_id,))

    student = cursor.fetchone()

    connection.close()

    if student:
        print("ID:", student[0])
        print("Name:", student[1])
        print("Age:", student[2])
        print("Address:", student[3])
    else:
        print("Student not found")

def update_student():
    student_id = int(input("Enter student ID to update: "))

    new_name = input("Enter new name: ")
    new_age = int(input("Enter new age: "))
    new_address = input("Enter new address: ")

    connection = connect_db()
    cursor = connection.cursor()

    cursor.execute("""
    UPDATE students
    SET name = ?, age = ?, address = ?
    WHERE id = ?
    """, (new_name, new_age, new_address, student_id))

    connection.commit()

    if cursor.rowcount == 0:
        print("Student not found")
    else:
        print("Student updated successfully")

    connection.close()

def delete_student():
    student_id = int(input("Enter student ID to delete: "))

    connection = connect_db()
    cursor = connection.cursor()

    cursor.execute("""
    DELETE FROM students
    WHERE id = ?
    """, (student_id,))

    connection.commit()

    if cursor.rowcount == 0:
        print("Student not found")
    else:
        print("Student deleted successfully")

    connection.close()

def menu():
    create_table()

    while True:
        print("\n===== Student Management System =====")
        print("1. Insert Student")
        print("2. View Students")
        print("3. Search Student")
        print("4. Update Student")
        print("5. Delete Student")
        print("6. Exit")

        choice = input("Enter your choice: ")

        if choice == "1":
            insert_student()

        elif choice == "2":
            view_students()

        elif choice == "3":
            search_student()

        elif choice == "4":
            update_student()

        elif choice == "5":
            delete_student()

        elif choice == "6":
            print("Program closed")
            break

        else:
            print("Invalid choice. Please try again")

menu()

16. Explanation of Complete Program

`connect_db()`

def connect_db():
    connection = sqlite3.connect("school.db")
    return connection

This function connects to the database.

We created a separate function so we do not need to write this again and again:

sqlite3.connect("school.db")

`create_table()`

This function creates the students table.

CREATE TABLE IF NOT EXISTS students

If the table already exists, it does not create another table.

`insert_student()`

This function adds a new student.

It takes input from user:

name = input("Enter student name: ")
age = int(input("Enter student age: "))
address = input("Enter student address: ")

Then inserts the data:

INSERT INTO students (name, age, address)
VALUES (?, ?, ?)

`view_students()`

This function shows all students.

SELECT * FROM students

This means:

Select all columns from students table.

`search_student()`

This function searches one student by ID.

SELECT * FROM students
WHERE id = ?

This means:

Find the student whose ID matches the given ID.

`update_student()`

This function updates student details.

UPDATE students
SET name = ?, age = ?, address = ?
WHERE id = ?

This means:

Change name, age, and address of the student whose ID matches.

`delete_student()`

This function deletes a student.

DELETE FROM students
WHERE id = ?

This means:

Delete the student whose ID matches.

17. Important SQL Keywords

Keyword	Meaning
`CREATE TABLE`	Creates a table
`INSERT INTO`	Adds data
`SELECT`	Reads data
`UPDATE`	Changes data
`DELETE`	Removes data
`WHERE`	Filters data
`ORDER BY`	Sorts data
`LIMIT`	Limits result

18. More SQL Examples

Show all students

SELECT * FROM students;

Show only name and age

SELECT name, age FROM students;

Search student by address

SELECT * FROM students
WHERE address = 'Kathmandu';

Sort students by age

SELECT * FROM students
ORDER BY age;

Show only first 5 students

SELECT * FROM students
LIMIT 5;

Delete all students carefully

DELETE FROM students;

This deletes all records, so use carefully.

19. Why We Use `?` in Python SQLite

We write:

cursor.execute("""
INSERT INTO students (name, age, address)
VALUES (?, ?, ?)
""", (name, age, address))

This is better than:

cursor.execute(f"""
INSERT INTO students (name, age, address)
VALUES ('{name}', {age}, '{address}')
""")

Why?

Because ? is safer.

It prevents many SQL errors and also helps protect from SQL injection.

For students, explain simply:

The question mark is an empty space. Python safely fills that empty space with the value we provide.

20. Common Mistakes

Mistake 1: Forgetting `commit()`

Wrong:

cursor.execute("INSERT INTO students (name, age, address) VALUES (?, ?, ?)", ("Ram", 18, "Kathmandu"))
connection.close()

Correct:

cursor.execute("INSERT INTO students (name, age, address) VALUES (?, ?, ?)", ("Ram", 18, "Kathmandu"))
connection.commit()
connection.close()

Without commit(), data may not be saved.

Mistake 2: Forgetting `WHERE` in UPDATE

Wrong:

UPDATE students
SET age = 20;

This changes age for all students.

Correct:

UPDATE students
SET age = 20
WHERE id = 1;

Mistake 3: Forgetting `WHERE` in DELETE

Wrong:

DELETE FROM students;

This deletes all students.

Correct:

DELETE FROM students
WHERE id = 1;

Mistake 4: Wrong Single Tuple

Wrong:

cursor.execute("DELETE FROM students WHERE id = ?", (student_id))

Correct:

cursor.execute("DELETE FROM students WHERE id = ?", (student_id,))

For one value, we need comma:

(student_id,)

21. Day 4 Practice Questions

SQL Practice

Create a table named products.
Add columns: id, name, price, quantity.
Insert three products.
Show all products.
Search product by ID.
Update product price.
Delete one product.

Python SQLite Practice

Create a product management system.

Requirements:

Create product table.
Add product.
View all products.
Search product.
Update product.
Delete product.
Use menu system.

Product table:

CREATE TABLE products (
    id INTEGER PRIMARY KEY AUTOINCREMENT,
    name TEXT NOT NULL,
    price REAL NOT NULL,
    quantity INTEGER NOT NULL
);

22. Product Management Practice Code Structure

Students should create functions like this:

def create_table():
    pass

def add_product():
    pass

def view_products():
    pass

def search_product():
    pass

def update_product():
    pass

def delete_product():
    pass

def menu():
    pass

This helps students practice functions and SQLite together.

23. Class Explanation Flow

You can teach in this order:

First revise file handling from Day 3.
Explain the problem with file handling.
Introduce database as a better storage system.
Explain table using Excel example.
Teach basic SQL commands.
Show SQLite connection in Python.
Explain cursor.
Create table.
Insert data.
Fetch data.
Update data.
Delete data.
Build complete CRUD app.
Give product management as practice.

24. Day 4 Final Summary

Today we learned:

Database

A database stores data in an organized way.

SQLite

SQLite is a simple database that stores data in a .db file.

SQL

SQL is the language used to talk with a database.

Cursor

Cursor is used to run SQL commands from Python.

CRUD

CRUD means:

Create
Read
Update
Delete

Important SQL Commands

CREATE TABLE
INSERT INTO
SELECT
UPDATE
DELETE
WHERE

Important Python SQLite Lines

import sqlite3

Used to use SQLite in Python.

sqlite3.connect("school.db")

Used to connect to database.

connection.cursor()

Used to create cursor.

cursor.execute()

Used to run SQL command.

connection.commit()

Used to save changes.

connection.close()

Used to close database.

Final Memory for Students

File handling stores data in files.

Database stores data in tables.

SQLite is a simple database.

SQL is used to talk with database.

Cursor runs SQL commands.

commit() saves changes.

CRUD means create, read, update, delete.

Day 3 Python Notes

Ankit Chapagain — Thu, 21 May 2026 15:35:56 GMT

Topics Covered

1. List Slicing
2. Tuple
3. Dictionary
4. Set
5. Exception Handling
6. Different Types of Exceptions
7. File Handling
8. Login System Using File Handling and Exception Handling

1. List Slicing

In Day 2, we learned about lists.

A list is used to store multiple values in one variable.

Example:

fruits = ["apple", "banana", "mango", "orange", "grapes"]

Now, we will learn list slicing.

List slicing means taking a specific part of a list.

List Index Revision

In Python, list index starts from 0.

Example:

fruits = ["apple", "banana", "mango", "orange"]

Index values:

apple   -> index 0
banana  -> index 1
mango   -> index 2
orange  -> index 3

Example:

fruits = ["apple", "banana", "mango", "orange"]

print(fruits[0])
print(fruits[1])

Output:

apple
banana

Basic List Slicing

Example:

numbers = [10, 20, 30, 40, 50]

print(numbers[0:3])

Output:

[10, 20, 30]

Explanation:

numbers[0:3]

means start from index 0 and stop before index 3.

It includes:

numbers[0]
numbers[1]
numbers[2]

It does not include index 3.

More List Slicing Examples

numbers = [10, 20, 30, 40, 50, 60]

print(numbers[0:3])
print(numbers[2:5])
print(numbers[:4])
print(numbers[3:])

Output:

[10, 20, 30]
[30, 40, 50]
[10, 20, 30, 40]
[40, 50, 60]

Explanation:

numbers[0:3]

starts from index 0 and stops before index 3.

numbers[2:5]

starts from index 2 and stops before index 5.

numbers[:4]

starts from the beginning and stops before index 4.

numbers[3:]

starts from index 3 and goes until the end.

Negative Indexing

Python also supports negative indexing.

Example:

fruits = ["apple", "banana", "mango", "orange"]

print(fruits[-1])
print(fruits[-2])

Output:

orange
mango

Explanation:

-1

means last item.

-2

means second last item.

Negative Slicing

Example:

numbers = [10, 20, 30, 40, 50, 60]

print(numbers[-3:])

Output:

[40, 50, 60]

Explanation:

numbers[-3:]

means take the last three items.

Slicing With Step

Example:

numbers = [10, 20, 30, 40, 50, 60]

print(numbers[0:6:2])

Output:

[10, 30, 50]

Explanation:

numbers[0:6:2]

means:

Start from index 0
Stop before index 6
Move by step 2

Reverse a List Using Slicing

Example:

numbers = [10, 20, 30, 40, 50]

print(numbers[::-1])

Output:

[50, 40, 30, 20, 10]

Explanation:

[::-1]

is used to reverse a list.

List Slicing Questions

Question 1

Print the first three items from a list.

Solution:

fruits = ["apple", "banana", "mango", "orange", "grapes"]

print(fruits[0:3])

Output:

['apple', 'banana', 'mango']

Question 2

Print the last two items from a list.

Solution:

fruits = ["apple", "banana", "mango", "orange", "grapes"]

print(fruits[-2:])

Output:

['orange', 'grapes']

Question 3

Reverse a list using slicing.

Solution:

numbers = [1, 2, 3, 4, 5]

print(numbers[::-1])

Output:

[5, 4, 3, 2, 1]

2. Tuple

A tuple is used to store multiple values in one variable.

It is similar to a list.

But the main difference is:

List is changeable.
Tuple is not changeable.

That means after creating a tuple, we cannot directly add, remove, or change its items.

Example:

fruits = ("apple", "banana", "mango")

print(fruits)

Output:

('apple', 'banana', 'mango')

Here, fruits is a tuple.

Accessing Tuple Items

Tuple index also starts from 0, just like list.

Example:

fruits = ("apple", "banana", "mango")

print(fruits[0])
print(fruits[1])
print(fruits[2])

Output:

apple
banana
mango

Explanation:

fruits[0]

gives "apple".

fruits[1]

gives "banana".

fruits[2]

gives "mango".

Tuple Cannot Be Changed

Example:

fruits = ("apple", "banana", "mango")

fruits[0] = "orange"

print(fruits)

This gives an error.

Because tuple does not allow item change.

Why Use Tuple?

We use tuple when we want to store values that should not change.

Example:

days = ("Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday")

Days of the week are fixed, so tuple is a good choice.

Another example:

location = (26.4525, 87.2718)

This can store latitude and longitude.

Looping Through Tuple

Example:

fruits = ("apple", "banana", "mango")

for fruit in fruits:
    print(fruit)

Output:

apple
banana
mango

Explanation:

Tuple is iterable.

So we can use a for loop to read each item one by one.

Tuple Question 1

Write a program to store five student names in a tuple and print them one by one.

Solution:

students = ("Ram", "Sita", "Hari", "Gita", "Shyam")

for student in students:
    print(student)

Output:

Ram
Sita
Hari
Gita
Shyam

Tuple Question 2

Write a program to find the length of a tuple.

Solution:

numbers = (10, 20, 30, 40, 50)

print("Total items:", len(numbers))

Output:

Total items: 5

Explanation:

len() counts how many items are inside the tuple.

Tuple Question 3

Write a program to check whether "apple" exists in a tuple or not.

Solution:

fruits = ("apple", "banana", "mango")

if "apple" in fruits:
    print("Apple exists")
else:
    print("Apple does not exist")

Output:

Apple exists

3. Dictionary

A dictionary is used to store data in key-value pairs.

Example:

student = {
    "name": "Ram",
    "age": 18,
    "address": "Kathmandu"
}

print(student)

Output:

{'name': 'Ram', 'age': 18, 'address': 'Kathmandu'}

Here:

"name"

is a key.

"Ram"

is the value.

Real-Life Example of Dictionary

A student has different details:

Name: Ram
Age: 18
Address: Kathmandu

In Python, we can store this like:

student = {
    "name": "Ram",
    "age": 18,
    "address": "Kathmandu"
}

Dictionary is useful when we want to store related information.

Accessing Dictionary Values

Example:

student = {
    "name": "Ram",
    "age": 18,
    "address": "Kathmandu"
}

print(student["name"])
print(student["age"])
print(student["address"])

Output:

Ram
18
Kathmandu

Explanation:

We use the key to access the value.

student["name"]

gives "Ram".

Updating Dictionary Value

Example:

student = {
    "name": "Ram",
    "age": 18
}

student["age"] = 19

print(student)

Output:

{'name': 'Ram', 'age': 19}

Explanation:

The value of "age" was changed from 18 to 19.

Adding New Key-Value Pair

Example:

student = {
    "name": "Ram",
    "age": 18
}

student["address"] = "Kathmandu"

print(student)

Output:

{'name': 'Ram', 'age': 18, 'address': 'Kathmandu'}

Explanation:

A new key "address" was added to the dictionary.

Removing Item from Dictionary

Example:

student = {
    "name": "Ram",
    "age": 18,
    "address": "Kathmandu"
}

student.pop("age")

print(student)

Output:

{'name': 'Ram', 'address': 'Kathmandu'}

Explanation:

pop() removes the item with the given key.

Looping Through Dictionary

Example:

student = {
    "name": "Ram",
    "age": 18,
    "address": "Kathmandu"
}

for key in student:
    print(key)

Output:

name
age
address

This prints only keys.

To print values:

student = {
    "name": "Ram",
    "age": 18,
    "address": "Kathmandu"
}

for key in student:
    print(student[key])

Output:

Ram
18
Kathmandu

To print both key and value:

student = {
    "name": "Ram",
    "age": 18,
    "address": "Kathmandu"
}

for key, value in student.items():
    print(key, ":", value)

Output:

name : Ram
age : 18
address : Kathmandu

Dictionary Question 1

Write a program to store student name, age, and address in a dictionary and print them.

Solution:

student = {
    "name": "Sita",
    "age": 19,
    "address": "Pokhara"
}

print("Name:", student["name"])
print("Age:", student["age"])
print("Address:", student["address"])

Output:

Name: Sita
Age: 19
Address: Pokhara

Dictionary Question 2

Write a program to store product name, price, and quantity. Then calculate total price.

Solution:

product = {
    "name": "Pen",
    "price": 20,
    "quantity": 5
}

total = product["price"] * product["quantity"]

print("Product:", product["name"])
print("Total price:", total)

Output:

Product: Pen
Total price: 100

Explanation:

Price is 20.

Quantity is 5.

So:

20 * 5 = 100

Dictionary Question 3

Write a program to update a student's marks.

Solution:

student = {
    "name": "Ram",
    "marks": 75
}

student["marks"] = 85

print(student)

Output:

{'name': 'Ram', 'marks': 85}

4. Set

A set is used to store multiple values in one variable.

But set has two important features:

1. Set does not allow duplicate values.
2. Set does not maintain fixed order.

Example:

numbers = {10, 20, 30, 40}

print(numbers)

Output may be:

{40, 10, 20, 30}

The order may be different.

That is normal in set.

Set Does Not Allow Duplicate Values

Example:

numbers = {10, 20, 20, 30, 30, 40}

print(numbers)

Output:

{40, 10, 20, 30}

Explanation:

Duplicate values are automatically removed.

Adding Item to Set

Example:

fruits = {"apple", "banana"}

fruits.add("mango")

print(fruits)

Output may be:

{'apple', 'banana', 'mango'}

The order may be different.

Removing Item from Set

Example:

fruits = {"apple", "banana", "mango"}

fruits.remove("banana")

print(fruits)

Output:

{'apple', 'mango'}

Looping Through Set

Example:

fruits = {"apple", "banana", "mango"}

for fruit in fruits:
    print(fruit)

Output may be:

banana
apple
mango

Explanation:

Set is iterable.

But the order is not fixed.

Why Use Set?

Set is useful when we want unique values only.

Example:

students = {"Ram", "Sita", "Ram", "Hari", "Sita"}

print(students)

Output:

{'Ram', 'Sita', 'Hari'}

Duplicate names are removed.

Set Question 1

Write a program to remove duplicate numbers from a list.

Solution:

numbers = [10, 20, 20, 30, 30, 40]

unique_numbers = set(numbers)

print(unique_numbers)

Output:

{40, 10, 20, 30}

Explanation:

The list contains duplicate values.

When we convert it into a set, duplicate values are removed.

Set Question 2

Write a program to add a new student name in a set.

Solution:

students = {"Ram", "Sita", "Hari"}

students.add("Gita")

print(students)

Output may be:

{'Ram', 'Sita', 'Hari', 'Gita'}

Set Question 3

Write a program to check whether "Ram" exists in a set or not.

Solution:

students = {"Ram", "Sita", "Hari"}

if "Ram" in students:
    print("Ram exists")
else:
    print("Ram does not exist")

Output:

Ram exists

5. Exception Handling

Exception handling means handling errors in a program.

Sometimes our program may get an error while running.

Example:

a = int(input("Enter first number: "))
b = int(input("Enter second number: "))

print(a / b)

If the user enters:

10
0

Then the program gives an error because division by zero is not allowed.

To handle this kind of error, we use:

try
except

Basic Try Except

Example:

try:
    a = int(input("Enter first number: "))
    b = int(input("Enter second number: "))

    result = a / b

    print("Result:", result)

except:
    print("Something went wrong")

Explanation:

The code that may cause an error is written inside try.

If an error happens, the code inside except runs.

So instead of crashing, the program shows a message.

Better Try Except

It is better to mention the exact error name.

Example:

try:
    a = int(input("Enter first number: "))
    b = int(input("Enter second number: "))

    result = a / b

    print("Result:", result)

except ZeroDivisionError:
    print("Cannot divide by zero")

except ValueError:
    print("Please enter numbers only")

Explanation:

ZeroDivisionError happens when we divide by zero.

ValueError happens when we enter invalid number input.

6. Different Types of Exceptions

Python has many types of exceptions.

Some common exceptions are:

1. ValueError
2. ZeroDivisionError
3. FileNotFoundError
4. IndexError
5. KeyError
6. TypeError
7. NameError
8. PermissionError

1. ValueError

ValueError happens when the value is not valid.

Example:

age = int("hello")

This gives an error because "hello" cannot be converted into an integer.

Correct handling:

try:
    age = int(input("Enter your age: "))
    print("Your age is", age)

except ValueError:
    print("Please enter a valid number")

2. ZeroDivisionError

ZeroDivisionError happens when we divide a number by zero.

Example:

try:
    a = 10
    b = 0

    result = a / b

    print(result)

except ZeroDivisionError:
    print("Cannot divide by zero")

Output:

Cannot divide by zero

3. FileNotFoundError

FileNotFoundError happens when we try to read a file that does not exist.

Example:

try:
    with open("data.txt", "r") as file:
        data = file.read()
        print(data)

except FileNotFoundError:
    print("File not found")

4. IndexError

IndexError happens when we try to access an index that does not exist in a list.

Example:

try:
    numbers = [10, 20, 30]

    print(numbers[5])

except IndexError:
    print("Index does not exist")

Output:

Index does not exist

Explanation:

The list has only three items.

Available indexes are:

0, 1, 2

But we tried to access index 5.

So IndexError happened.

5. KeyError

KeyError happens when we try to access a dictionary key that does not exist.

Example:

try:
    student = {
        "name": "Ram",
        "age": 18
    }

    print(student["address"])

except KeyError:
    print("Key does not exist")

Output:

Key does not exist

Explanation:

The dictionary has only:

name
age

But we tried to access:

address

So KeyError happened.

6. TypeError

TypeError happens when we perform an operation with the wrong data type.

Example:

try:
    result = "Age: " + 20
    print(result)

except TypeError:
    print("Cannot add string and number directly")

Output:

Cannot add string and number directly

Correct way:

result = "Age: " + str(20)
print(result)

7. NameError

NameError happens when we use a variable that has not been created.

Example:

try:
    print(username)

except NameError:
    print("Variable is not defined")

Output:

Variable is not defined

8. PermissionError

PermissionError happens when Python does not have permission to read or write a file.

Example:

try:
    with open("/root/data.txt", "w") as file:
        file.write("Hello")

except PermissionError:
    print("You do not have permission to write this file")

Handling Multiple Exceptions Together

Example:

try:
    a = int(input("Enter first number: "))
    b = int(input("Enter second number: "))

    result = a / b

    print("Result:", result)

except ValueError:
    print("Please enter numbers only")

except ZeroDivisionError:
    print("Cannot divide by zero")

except Exception as e:
    print("Something went wrong:", e)

Explanation:

ValueError handles invalid input.

ZeroDivisionError handles division by zero.

Exception handles any other unexpected error.

Try Except Else

else runs only when there is no error.

Example:

try:
    age = int(input("Enter your age: "))

except ValueError:
    print("Please enter a valid number")

else:
    print("Your age is", age)

Explanation:

If the user enters a correct number, else runs.

If the user enters text like "abc", except runs.

Try Except Finally

finally always runs.

Example:

try:
    number = int(input("Enter a number: "))
    print(number)

except ValueError:
    print("Invalid input")

finally:
    print("Program finished")

Explanation:

Whether error happens or not, finally runs.

7. File Handling

File handling means working with files using Python.

Using file handling, we can:

1. Create a file
2. Write data into a file
3. Read data from a file
4. Add new data into an existing file

Opening a File

Python uses open() to open a file.

Syntax:

file = open("filename.txt", "mode")

Common file modes:

"r"  read mode
"w"  write mode
"a"  append mode

Write Mode

Write mode is used to write data into a file.

Example:

file = open("student.txt", "w")

file.write("Hello, this is my first file.")

file.close()

Explanation:

student.txt is the file name.

"w" means write mode.

write() writes data into the file.

close() closes the file.

Important:

If the file does not exist, Python creates it.

If the file already exists, write mode replaces old content.

Reading a File

Example:

file = open("student.txt", "r")

data = file.read()

print(data)

file.close()

Output:

Hello, this is my first file.

Explanation:

"r" means read mode.

read() reads the file content.

Append Mode

Append mode is used to add new data without deleting old data.

Example:

file = open("student.txt", "a")

file.write("\nThis is new line.")

file.close()

Explanation:

"a" means append mode.

It adds new content at the end of the file.

\n means new line.

Better Way: Using with open()

The better way to work with files is:

with open("student.txt", "w") as file:
    file.write("Hello Python")

Here, we do not need to write:

file.close()

Python automatically closes the file.

Read File Using with open()

Example:

with open("student.txt", "r") as file:
    data = file.read()
    print(data)

File Handling With Exception Handling

File handling and exception handling are often used together.

Why?

Because file errors can happen.

For example:

1. File may not exist.
2. User may enter wrong input.
3. Program may not have permission to read/write file.

Example:

try:
    with open("student.txt", "r") as file:
        data = file.read()
        print(data)

except FileNotFoundError:
    print("File does not exist")

Explanation:

If student.txt exists, Python reads the file.

If it does not exist, FileNotFoundError happens.

Then except block runs.

8. File-Based Login System

Now we will create a simple login system using file handling.

In this system:

Each user will have their own file.
The username will be used as the file name.
The password will be saved inside that file.

Example:

If username is:

ram

Then Python creates:

ram.txt

Inside ram.txt, the password is saved.

Full Login System Code

def register():
    username = input("Enter your username: ")
    password = input("Enter your password: ")

    try:
        file = open(f"{username}.txt", "r")
        print("Username already exists")
        file.close()

    except FileNotFoundError:
        with open(f"{username}.txt", "w") as f:
            f.write(password)

        print("User registered successfully")

    except Exception as e:
        print("Something went wrong while registering:", e)


def login():
    username = input("Enter your username: ")
    password = input("Enter your password: ")

    try:
        file = open(f"{username}.txt", "r")
        file.close()

    except FileNotFoundError:
        print("User not found")
        return

    except Exception as e:
        print("Something went wrong while opening user file:", e)
        return

    try:
        with open(f"{username}.txt", "r") as f:
            checkpass = f.readline()

            if password == checkpass:
                print("Welcome")
            else:
                print("Sorry, incorrect password")

    except Exception as e:
        print("Something went wrong while checking password:", e)


def ask():
    x = input("Do you want to register or login? Press r for register and l for login: ")

    if x == "r":
        register()

    elif x == "l":
        login()

    else:
        print("Invalid choice")


ask()

9. Explanation of Login System

Register Function

def register():

This function is used to register a new user.

username = input("Enter your username: ")
password = input("Enter your password: ")

Here, the program asks the user to enter username and password.

Checking If Username Already Exists

try:
    file = open(f"{username}.txt", "r")
    print("Username already exists")
    file.close()

Here, the program tries to open a file with the username.

Example:

If username is:

ram

Then it tries to open:

ram.txt

If the file exists, it means the username is already registered.

So the program prints:

Username already exists

Creating File for New User

except FileNotFoundError:
    with open(f"{username}.txt", "w") as f:
        f.write(password)

    print("User registered successfully")

If the file does not exist, Python gives FileNotFoundError.

That means the username is new.

So the program creates a new file and saves the password inside it.

Example:

If username is:

sita

Then file name becomes:

sita.txt

And inside that file, the password is saved.

Login Function

def login():

This function is used to login an existing user.

username = input("Enter your username: ")
password = input("Enter your password: ")

The program asks for username and password.

Checking If User Exists

try:
    file = open(f"{username}.txt", "r")
    file.close()

The program tries to open the user's file.

If the file exists, the user exists.

User Not Found

except FileNotFoundError:
    print("User not found")
    return

If the file does not exist, the program prints:

User not found

Here, return is used to stop the function.

This is better than exit() because exit() closes the whole program immediately.

Reading Saved Password

with open(f"{username}.txt", "r") as f:
    checkpass = f.readline()

This opens the user's file and reads the saved password.

The saved password is stored in:

checkpass

Checking Password

if password == checkpass:
    print("Welcome")
else:
    print("Sorry, incorrect password")

If entered password and saved password are same, login is successful.

Otherwise, it prints incorrect password.

10. Simpler Version Like Your Original Code

This is very close to your original code.

def register():
    username = input("Enter your username: ")
    password = input("Enter your password: ")

    try:
        file = open(f"{username}.txt", "r")
        print("Username already exists")
        file.close()

    except:
        with open(f"{username}.txt", "w") as f:
            f.write(password)

        print("User registered successfully")


def login():
    username = input("Enter your username: ")
    password = input("Enter your password: ")

    try:
        file = open(f"{username}.txt", "r")
        file.close()

    except:
        print("User not found")
        return

    with open(f"{username}.txt", "r") as f:
        checkpass = f.readline()

        if password == checkpass:
            print("Welcome")
        else:
            print("Sorry, incorrect password")


def ask():
    x = input("Do you want to register or login? Press r for register and l for login: ")

    if x == "r":
        register()
    else:
        login()


ask()

This version is okay for beginners.

But for better practice, this is preferred:

except FileNotFoundError:

instead of only:

except:

Because except: catches all errors, but FileNotFoundError catches only file-not-found error.

11. Important Note About This Login System

This login system is only for learning.

It teaches:

1. Function
2. Input
3. File handling
4. Try and except
5. User already exists
6. User not found
7. Password checking

But in real websites or real applications, passwords should not be saved directly like this.

In real projects, passwords should be hashed before saving.

For now, this is good for beginner-level Python file handling practice.

12. Class Explanation Flow

You can explain the login system like this:

When registering:
Python checks if username.txt exists.
If it exists, the user already exists.
If it does not exist, Python creates the file and saves the password.

When logging in:
Python checks if username.txt exists.
If it does not exist, user not found.
If it exists, Python reads the saved password.
Then it compares the saved password with the entered password.

13. Day 3 Practice Questions

List Slicing Questions

Create a list of 10 numbers and print the first 5 numbers.
Print the last 3 numbers from a list.
Reverse a list using slicing.
Print every second item from a list.

Tuple Questions

Create a tuple of five fruits and print each fruit.
Create a tuple of numbers and find its length.
Check whether "Python" exists in a tuple.
Try to change a tuple item and observe the error.

Dictionary Questions

Create a dictionary for a student with name, age, class, and address.
Create a dictionary for a product and calculate total price.
Update the marks of a student in a dictionary.
Print all keys and values from a dictionary.

Set Questions

Create a set of numbers with duplicate values and print it.
Add a new item to a set.
Remove an item from a set.
Convert a list with duplicate values into a set.

Exception Handling Questions

Take two numbers and divide them. Handle ZeroDivisionError.
Take age from user. Handle ValueError.
Try to access an invalid list index. Handle IndexError.
Try to access an invalid dictionary key. Handle KeyError.
Try to read a file that does not exist. Handle FileNotFoundError.

File Handling Questions

Create a file named message.txt and write "Hello Python" into it.
Read and print the content of message.txt.
Append three student names into students.txt.
Read a file and handle FileNotFoundError.

Final Project Question

Create a login system using file handling.

Requirements:

1. Register user.
2. Login user.
3. If user already exists, show message.
4. If user does not exist, show user not found.
5. If password is correct, show welcome.
6. If password is wrong, show incorrect password.
7. Use try and except.
8. Store each user password in username.txt file.

14. Day 3 Final Summary

Today we learned:

List slicing:
Used to get part of a list.

Tuple:
Used to store multiple values that should not change.

Dictionary:
Used to store data in key-value pairs.

Set:
Used to store unique values.

Exception handling:
Used to handle errors without crashing the program.

File handling:
Used to create, read, write, and append files.

Login system:
Used file handling and exception handling together.

Final simple memory:

List      -> changeable collection
Tuple     -> unchangeable collection
Dictionary -> key-value collection
Set       -> unique value collection
try-except -> error handling
File      -> permanent data storage

Introduction to Programming and Python Day-1

Ankit Chapagain — Tue, 19 May 2026 12:21:56 GMT

1. What is Programming?

Programming is the process of giving instructions to a computer so that it can perform a task.

A computer is a powerful machine, but it cannot think or work by itself. It needs clear instructions from humans.

Programming is mainly about solving problems and getting the expected output from the computer.

Example tasks done by programming:

Calculating marks
Creating a bill
Storing student records
Making websites
Automating repeated work

2. What is a Program?

A program is a set of instructions written to perform a specific task.

For example, if we want a computer to calculate the total price of products, we write instructions for it. Those instructions together are called a program.

In simple words:

Program = instructions given to the computer

3. What is a Programming Language?

A programming language is a language used to write programs.

Computers understand machine language, which is based on 0 and 1. But writing in 0 and 1 is very difficult for humans.

So, programming languages are used to write instructions in a human-friendly way.

Examples of programming languages:

Python
C
C++
Java
JavaScript

4. Program, Programming, and Programming Language

Term	Meaning
Program	Set of instructions
Programming	Process of writing instructions
Programming Language	Language used to write instructions

Example:

A calculator app is a program.

Creating that calculator app is programming.

Using Python to create it means Python is the programming language.

5. Why Do We Need Programming?

We need programming to make computers perform tasks automatically, quickly, and accurately.

Without programming, computers cannot do useful work by themselves.

Programming is used to:

Solve problems
Save time
Reduce human errors
Automate repeated tasks
Build software, apps, and websites

6. What is Programming Paradigm?

A programming paradigm is a style or method of writing programs.

It means how we organize and write our code to solve a problem.

Main programming paradigms are:

Procedural Programming
Object-Oriented Programming
Functional Programming

7. Procedural Programming

Procedural programming is a style of programming where instructions are written step by step.

It focuses on procedures or functions.

In simple words:

Do this first, then do that, then show the result.

It is useful for simple and step-by-step programs.

Example tasks:

Calculating total marks
Finding simple interest
Printing a bill

8. Object-Oriented Programming

Object-Oriented Programming, or OOP, is a style of programming based on objects.

An object represents a real-world thing.

Examples of objects:

Student
Car
Bank account
Product
Customer

Each object has properties and actions.

For example, a student can have:

Properties:

Name
Age
Roll number

Actions:

Study
Attend class
Give exam

OOP is useful for organizing large programs.

9. Functional Programming

Functional programming is a style of programming where problems are solved mainly using functions.

A function takes input, processes it, and gives output.

In simple words:

Input → Function → Output

Functional programming is useful when we want clean and predictable results.

10. What is Python?

Python is a high-level, general-purpose programming language.

It is used to create different types of programs and applications.

Python is popular because it is simple, readable, and beginner-friendly.

Python was created by Guido van Rossum and first released in 1991.

11. Why Python?

Python is used because:

Easy to learn
Python is simple and readable, so beginners can understand it easily.
Beginner-friendly
Students can focus more on logic instead of complex syntax.
Used in many fields
Python is used in web development, automation, data analysis, AI, and software development.
Large library support
Python has many ready-made libraries that help developers work faster.
Strong community support
Python has a large community, so learning materials and solutions are easily available.

12. Introduction to Python

Python is a programming language used to give instructions to a computer.

It is called a high-level language because it is easier for humans to read and write.

Python is also an interpreted language, which means Python runs code line by line.

Python files usually have the extension:

.py

Example:

main.py

13. Features of Python

Main features of Python are:

Simple and easy to read
Free and open-source
Works on Windows, Linux, and macOS
Has many libraries
Supports different programming styles

14. Where is Python Used?

Python is used in many areas, such as:

Web development
Data analysis
Artificial intelligence
Automation
Software development

Memory Management

1. What is Memory Management?

Memory management means how a programming language stores, uses, and removes data from computer memory while a program is running.

When we create variables, objects, lists, strings, or functions, they need space in memory.

Python manages most of this memory automatically, so the programmer does not need to manually allocate and delete memory like in some other languages.

2. Why Memory Management is Needed?

Memory management is needed because:

Programs need memory to store data.
Unused data should be removed from memory.
Memory should be used efficiently.
Programs should not become slow because of unnecessary memory usage.
It helps avoid memory-related errors.

3. Stack Memory

Stack memory is used to store temporary information during program execution.

It mainly stores:

Function calls
Local variables
References to objects

Stack works in a last in, first out order.

That means the function that is called last will finish first.

Example idea:

Function starts → memory is added to stack
Function ends → memory is removed from stack

Stack memory is fast and temporary.

4. Heap Memory

Heap memory is used to store objects and data created during program execution.

In Python, actual objects are stored in heap memory.

Examples of objects stored in heap:

Numbers
Strings
Lists
Dictionaries
Custom objects

Heap memory is larger than stack memory and is used for data that may be needed for a longer time.

5. Garbage Collection

Garbage collection is the process of removing unused objects from memory.

When an object is no longer needed and no variable refers to it, Python automatically removes it from memory.

Example:

a = [1, 2, 3]
a = "Hello"

At first, a refers to the list [1, 2, 3].

Later, a refers to "Hello".

Now, if no other variable refers to [1, 2, 3], Python can remove that list from memory.

This automatic cleaning process is called garbage collection.

Python Installation and Virtual Environment Setup

1. Installing Python

Python must be installed before we can write and run Python programs.

To check whether Python is already installed, open terminal or command prompt and type:

python --version

python3 --version

If Python is installed, it will show the version.

Example:

Python 3.x.x

2. Installing Python on Windows

Step 1: Download Python

Go to the official Python website and download Python for Windows.

Step 2: Run the installer

Open the downloaded installer.

Very important:

Tick/Add: Add Python to PATH

Then click:

Install Now

Step 3: Check installation

Open Command Prompt and type:

python --version

Also check pip:

pip --version

pip is used to install Python packages.

3. Installing Python on macOS

macOS may already have Python installed, but it is better to install the latest Python 3 version.

Option 1: Install from official website

Download Python for macOS from the official Python website and install it.

Then check:

python3 --version

Check pip:

pip3 --version

Option 2: Install using Homebrew

If Homebrew is installed, use:

brew install python

Then check:

python3 --version

4. Installing Python on Linux

Most Linux systems already have Python installed.

Check using:

python3 --version

If Python is not installed, install it using the package manager.

Ubuntu/Debian

sudo apt update
sudo apt install python3 python3-pip python3-venv

Check installation:

python3 --version
pip3 --version

5. What is pip?

pip is the package manager for Python.

It is used to install external Python packages.

Example:

pip install django

or on macOS/Linux:

pip3 install django

Packages are ready-made tools or libraries that help us build projects faster.

6. What is a Virtual Environment?

A virtual environment is a separate workspace for a Python project.

It allows each project to have its own packages and dependencies.

In simple words:

Virtual environment = separate Python setup for one project

7. Why Do We Need a Virtual Environment?

We need a virtual environment because different projects may need different package versions.

Example:

Project A needs Django 4
Project B needs Django 5

If we install everything globally, there may be conflicts.

A virtual environment solves this problem by keeping packages separate for each project.

8. Benefits of Virtual Environment

Keeps each project separate
Avoids package version conflicts
Keeps the main system clean
Makes projects easier to share
It is a professional Python practice

9. Creating a Project Folder

First, create a folder for your project.

Windows

mkdir my_project
cd my_project

macOS/Linux

mkdir my_project
cd my_project

10. Creating Virtual Environment

Windows

python -m venv venv

macOS/Linux

python3 -m venv venv

Here:

python -m venv means create a virtual environment.
venv is the name of the virtual environment folder.

You can use another name, but venv is commonly used.

11. Activating Virtual Environment

After creating the virtual environment, we need to activate it.

Windows

venv\Scripts\activate

macOS/Linux

source venv/bin/activate

After activation, you will see:

(venv)

Example:

(venv) my_project>

This means the virtual environment is active.

12. Installing Packages Inside Virtual Environment

After activating the virtual environment, install packages normally.

Example:

pip install requests

or:

pip install django

These packages will be installed only inside that project's virtual environment.

They will not affect other projects.

13. Checking Installed Packages

To see installed packages:

pip list

This shows the packages installed inside the active virtual environment.

14. Saving Packages

To save installed packages in a file:

pip freeze > requirements.txt

This creates a file named:

requirements.txt

It contains the list of packages used in the project.

15. Installing Packages from requirements.txt

When someone shares a Python project, they usually share a requirements.txt file.

To install all required packages:

pip install -r requirements.txt

16. Deactivating Virtual Environment

To close the virtual environment:

deactivate

After this, (venv) disappears from the terminal.

17. Common Python Project Setup Flow

Windows

mkdir my_project
cd my_project
python -m venv venv
venv\Scripts\activate
pip install package_name
pip freeze > requirements.txt
deactivate

macOS/Linux

mkdir my_project
cd my_project
python3 -m venv venv
source venv/bin/activate
pip install package_name
pip freeze > requirements.txt
deactivate

First Code in Python

After installing Python and setting up the virtual environment, the first program we usually write is:

print("Hello, World!")

Ankit

Arduino Height Measurement System

1. Project Overview

Technologies Used

System Architecture

2. Hardware Requirements

3. Hardware Connections

HC-SR04 to Arduino UNO

4. Arduino IDE Setup

Step 1: Install Arduino IDE

Step 2: Arduino Code

Step 3: Upload the Program

5. Python Environment Setup

Step 1: Install Python

Step 2: Create Project Folder

Step 3: Create Python Virtual Environment

Step 4: Activate Virtual Environment

Step 5: Install Required Libraries

6. Project Structure

7. Create the Python Application

Person's Height

Sensor Distance

Sensor Mounting Height

-- cm

Arduino Status: Checking...

8. Configure Sensor Height and COM Port

9. Run the Application

Example Result

10. Troubleshooting

11. Important Accuracy and Safety Notes

12. Future Improvements

Arduino DHT11 Temperature & Humidity Monitoring System

1. Project Overview

Technologies Used

System Architecture

2. Hardware Requirements

DHT11 Connections

3. Arduino IDE Setup

Step 1: Install Arduino IDE

Step 2: Install DHT11 Library

Step 3: Arduino Code

Expected Serial Output

4. Python Environment Setup

Step 1: Install Python

Step 2: Create Project Folder

Step 3: Create Python Virtual Environment

Step 4: Activate Virtual Environment

Step 5: Install Required Libraries

Step 6: Save Dependencies

5. Project Structure

6. Create the Python Application

Temperature

Humidity

Arduino Status: Checking...

7. Configure Arduino COM Port

8. Run the Application

9. Troubleshooting

10. Useful Commands

11. Future Improvements

Arduino Height Measurement System

1. Project Overview

Technologies Used

System Architecture

2. Hardware Requirements

3. Hardware Connections

HC-SR04 to Arduino UNO

4. Arduino IDE Setup

Step 1: Install Arduino IDE

Step 2: Arduino Code

Step 3: Upload the Program

5. Python Environment Setup

Step 1: Install Python

Step 2: Create Project Folder

Step 3: Create Python Virtual Environment

Step 4: Activate Virtual Environment

Step 5: Install Required Libraries

6. Project Structure

7. Create the Python Application

Person's Height

Sensor Distance