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Flask Cheat Sheet

Here’s a basic cheat sheet for Flask, a popular Python web framework.

Table of Contents

Setup

  1. Install Flask:

    pip install Flask

  2. Basic Application:

    from flask import Flask

app = Flask(__name__)

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

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

Routing

  • Basic Route:

    @app.route('/path')
def function_name():
    return 'Response'

  • Dynamic Routes:

    @app.route('/user/<username>')
def show_user_profile(username):
    return f'User {username}'

  • HTTP Methods:

    @app.route('/post', methods=['POST'])
def handle_post():
    return 'POST request'

Request and Response

  • Access Request Data:

    from flask import request

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

  • JSON Request:

    @app.route('/json', methods=['POST'])
def json_example():
    data = request.json
    return f"Received data: {data}"

  • Response Object:

    from flask import make_response

@app.route('/response')
def custom_response():
    response = make_response('Custom response')
    response.headers['X-Custom-Header'] = 'Value'
    return response

Templates

  • Render Template:

    from flask import render_template

@app.route('/hello')
def hello():
    return render_template('hello.html', name='World')

    In templates/hello.html:

    <!doctype html>
<html>
    <head><title>Hello</title></head>
    <body>
        <h1>Hello {{ name }}!</h1>
    </body>
</html>

Static Files

  • Serve Static Files:
    • Place static files (CSS, JS) in a folder named static.
    • Access static files via /static/filename.

Blueprints

  • Create and Register Blueprint: 
    from flask import Blueprint

example_bp = Blueprint('example', __name__)

@example_bp.route('/example')
def example():
    return 'Blueprint example'

app.register_blueprint(example_bp)

Error Handling

  • Custom Error Pages: 
    @app.errorhandler(404)
def not_found_error(error):
    return 'Page not found', 404

@app.errorhandler(500)
def internal_error(error):
    return 'Internal server error', 500

Sessions

  • Using Sessions: 
    from flask import session

app.secret_key = 'supersecretkey'

@app.route('/set_session')
def set_session():
    session['username'] = 'admin'
    return 'Session data set'

@app.route('/get_session')
def get_session():
    username = session.get('username', 'not set')
    return f'Username is {username}'

Debugging

  • Enable Debug Mode: 
    if __name__ == '__main__':
    app.run(debug=True)

This cheat sheet covers the basics of Flask, but Flask has many more capabilities that can be explored through its official documentation.