Flask Cheat Sheet

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

Installation

pip install Flask

Hello World App

from flask import Flask

app = Flask(__name__)

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

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

Routing

@app.route('/route')
def my_route():
    return 'This is my route!'

Variable Rules

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

HTTP Methods

from flask import request

@app.route('/login', methods=['POST', 'GET'])
def login():
    if request.method == 'POST':
        # Process login data
        return 'Login POST request'
    else:
        return 'Login GET request'

Templates

Create a templates folder in your project directory.

Use the render_template function to render HTML templates.

Forms

Use the Flask-WTF extension for form handling.

• Example:

from flask_wtf import FlaskForm
from wtforms import StringField, SubmitField

class MyForm(FlaskForm):
    name = StringField('Name')
    submit = SubmitField('Submit')

Redirects and Errors

from flask import redirect, url_for, abort

@app.route('/redirect')
def my_redirect():
    return redirect(url_for('my_route'))

@app.route('/error')
def my_error():
    abort(404)

Flask Extensions

• Flask offers various extensions for additional functionality.
• Example: Flask-SQLAlchemy, Flask-Login, Flask-Mail.

Static Files

• Create a static folder in your project directory.
• Use the url_for function to link to static files.
• Example:

<link rel="stylesheet" href="{{ url_for('static', filename='style.css') }}">

Flask CLI

Run the Flask development server with:

flask run

Create database tables with:

flask db init
flask db migrate
flask db upgrade

Deployment

Common deployment options include Gunicorn, uWSGI, or using a platform like Heroku.

This cheat sheet covers some fundamental concepts in Flask. Remember to refer to the Flask documentation for more in-depth information and advanced features.