Flask Cheatsheet with Example and Definition

6 October 2023

Flask, a micro web framework for Python, has gained immense popularity for its simplicity and flexibility. Whether you’re a novice or an experienced developer, this Flask Cheatsheet will be your invaluable companion. It offers clear definitions, practical examples, and tips to help you master Flask and streamline web development.

Introduction to Flask

Flask is a lightweight web framework for Python that makes it easy to build web applications. It provides the tools you need to get your web project up and running quickly.

Setting Up Flask

Get started with Flask:

Installing Flask

pip install Flask

Creating a Flask Application

from flask import Flask
app = Flask(__name__)

Routes and Views

Define routes and views for your application:

Defining Routes

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

Creating Views

@app.route('/about')
def about():
    return 'About Us'

Dynamic Routes

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

Templates and HTML Rendering

Render HTML templates with Flask:

Rendering HTML

from flask import render_template

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

Template Inheritance

<!-- base.html -->
<!DOCTYPE html>
<html>
<head>
    <title>{% block title %}{% endblock %}</title>
</head>
<body>
    <div id="content">{% block content %}{% endblock %}</div>
</body>
</html>

Handling Forms

Process user input with Flask:

Creating Forms

from flask_wtf import FlaskForm
from wtforms import StringField, SubmitField

class SearchForm(FlaskForm):
    query = StringField('Search Query')
    submit = SubmitField('Search')

Processing Form Data

@app.route('/search', methods=['POST'])
def search():
    form = SearchForm()
    if form.validate_on_submit():
        query = form.query.data
        # process query

Database Integration

Integrate databases with Flask:

SQLAlchemy Setup

from flask_sqlalchemy import SQLAlchemy

app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///mydatabase.db'
db = SQLAlchemy(app)

Database Models

class User(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    username = db.Column(db.String(80), unique=True, nullable=False)

Querying the Database

user = User.query.filter_by(username='john').first()

User Authentication

Implement user authentication:

User Login System

from flask_login import LoginManager, UserMixin, login_user, login_required

login_manager = LoginManager()
login_manager.init_app(app)

@login_manager.user_loader
def load_user(user_id):
    return User.query.get(int(user_id))

Password Hashing

from werkzeug.security import generate_password_hash, check_password_hash

hashed_password = generate_password_hash('password', method='sha256')

Middleware and Extensions

Enhance your application with middleware and extensions:

Using Middleware

from flask import Flask, request

@app.before_request
def before_request():
    if not request.is_secure:
        return 'Use HTTPS for secure connection', 400

Flask Extensions

from flask_mail import Mail

mail = Mail(app)

Deployment and Production

from flask_mail import Mail

mail = Mail(app)

Prepare your Flask application for production:

Preparing for Production

  • Debug mode off
  • Secret key
  • Secure database configuration

Deployment Options

  • uWSGI
  • Gunicorn
  • Docker

Error Handling and Debugging

Handle errors gracefully and debug effectively:

Error Pages

@app.errorhandler(404)
def page_not_found(e):
    return 'Page not found', 404

Debugging Techniques

  • print statements
  • Flask Debug Toolbar
  • Logging

Best Practices

Adopt best practices for Flask development:

Code Organization

/app
    /templates
    /static
/config.py
/app.py

Security Measures

  • Protect against SQL injection
  • Secure password storage
  • Cross-Site Request Forgery (CSRF) protection

Conclusion

Flask is a powerful yet straightforward web framework for Python. This cheatsheet equips you with essential Flask concepts, from setting up your application to advanced topics like database integration and deployment. Whether you’re building a simple web app or a complex system, Flask’s flexibility and simplicity make it a valuable tool for web development.