Topic 1

What is Flask?
- Flask is a lightweight, micro web framework written in Python.
- It’s considered “micro” because it doesn’t come with built-in tools and libraries like some larger frameworks (e.g., Django). This means you can add only what you need, making it flexible and efficient.
Why use Flask?
- It’s Pythonic, minimalistic, and quick to get started with.
- Great for small to medium-sized web applications, RESTful services, and prototypes.

pip install Flask

Hello World in Flask

from flask import Flask
app = Flask(__name__)

@app.route('/')
def hello_world():
return 'Hello, World!'

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

Routes define the URLs that your application implements and the views that should be triggered when those URLs are accessed.
Basic routing
python
@app.route('/hello') def hello(): return 'Hello Flask!'
Variable rules
python
@app.route('/user/<username>') def show_user_profile(username): return f'User {username}'

Flask uses the Jinja2 template engine, allowing you to send dynamic data and render it on HTML templates.
Setting up a template
1. Create a folder named templates in your project directory.
2. Create an HTML file within this folder, e.g., index.html.
html
<h1>Hello, {{ name }}!</h1>
- Rendering a template
python
from flask import render_template @app.route('/hello/<name>') def hello_name(name): return render_template('index.html', name=name)

Flask uses the Jinja2 template engine, allowing you to send dynamic data and render it on HTML templates.
Setting up a template
1. Create a folder named templates in your project directory.
2. Create an HTML file within this folder, e.g., index.html.
html
<h1>Hello, {{ name }}!</h1>
- Rendering a template
python
from flask import render_template @app.route('/hello/<name>') def hello_name(name): return render_template('index.html', name=name)

For CSS, JavaScript, images, etc., Flask serves static files from the static folder.
Using static files
html
<link rel="stylesheet" href="{{ url_for('static', filename='style.css') }}">