Basic Understanding of Flask (For Beginners)

 

1. What is Flask?

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

👉 In simple terms:
Flask = a tool that helps you create websites using Python

2. Why Use Flask?

Flask is:

• Simple and beginner-friendly
• Lightweight (not complex)
• Flexible (you can build anything from small to big apps)
• Great for learning backend development

3. What is a Web Framework?

A web framework is a tool that:

• Helps you handle web requests
• Connects your code to the browser
• Makes building websites easier

👉 Without Flask, building a web app from scratch is difficult.

4. How Flask Works

👉 Flow:

1. User opens a website in browser
2. Browser sends request to server
3. Flask processes the request
4. Flask returns a response (HTML page)
5. Browser displays it

5. Installing Flask

Step 1: Install Python

Download from: python.org

Step 2: Install Flask

Open terminal and run:

pip install flask

6. Your First Flask App

from flask import Flask

app = Flask(__name__)

@app.route('/')
def home():
    return "Hello, Flask!"

if __name__ == '__main__':
    app.run(debug=True)

👉 Run this and open:
http://127.0.0.1:5000

7. Understanding the Code

• Flask(__name__) → Creates the app
• @app.route('/') → Defines the homepage
• def home() → Function for the page
• return → What is shown in browser

8. Routing (Creating Pages)

@app.route('/about')
def about():
    return "This is the about page"

👉 Visit:

• / → Home
• /about → About page

9. Using HTML with Flask (Templates)

Flask uses HTML files to display pages.

Folder structure:

project/
│
├── app.py
└── templates/
    └── index.html

HTML (templates/index.html):

<h1>Welcome to my website</h1>

Python:

from flask import render_template

@app.route('/')
def home():
    return render_template('index.html')

10. Passing Data to HTML

@app.route('/user/<name>')
def user(name):
    return f"Hello {name}"

👉 Visit:
/user/Daniel → Output: Hello Daniel

11. Forms in Flask (User Input)

from flask import request

@app.route('/submit', methods=['POST'])
def submit():
    name = request.form['name']
    return f"Hello {name}"

12. Flask vs Django (Simple Comparison)

Feature	Flask	Django
Complexity	Simple	More complex
Flexibility	High	Structured
Best for	Beginners, small apps	Large applications

13. Real-Life Uses of Flask

Students can use Flask to:

• Build personal websites
• Create login systems
• Develop dashboards
• Build APIs
• Create simple web apps
• Connect Python to websites

14. Simple Project Idea (For Students)

👉 Build:

• Personal portfolio website
• Simple blog
• Student registration system
• Contact form website

15. Flask in Web Development

👉 Full stack view:

• HTML → Structure
• CSS → Design
• JavaScript → Interactivity
• Flask (Python) → Backend logic

16. Simple Summary

👉 Flask helps you:

• Use Python for web development
• Build dynamic websites
• Handle user requests and data

Power Teaching Line (for your class)

👉 “Flask is the bridge that connects Python to the web.”