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Pragmatic AI Stack
Alternatives Web Framework

Flask

Alternative

Lightweight WSGI web application framework

Difficulty
Beginner
Category
Web Framework
Alternative to
FastAPI
Reading Time
4 min
GitHub Documentation

Strengths

  • Simple and minimalist design
  • Large ecosystem of extensions
  • Mature and stable
  • Flexible and unopinionated

Considerations

  • No built-in async support
  • Manual type checking
  • No automatic API documentation

Best Use Cases

  • Simple web applications
  • Prototyping
  • Traditional web apps with templates

Flask

Flask is a lightweight WSGI web application framework. It is designed to make getting started quick and easy, with the ability to scale up to complex applications. It began as a simple wrapper around Werkzeug and Jinja and has become one of the most popular Python web application frameworks.

Why Choose Flask Over FastAPI?

While FastAPI is our core stack recommendation, Flask might be the better choice if:

  • Simplicity is key: You need a minimal framework without the complexity of async programming
  • Template-based apps: You’re building traditional web applications with server-side rendering
  • Learning curve: You’re new to web development and want to start with something simple
  • Existing ecosystem: You need to integrate with Flask-specific extensions

Key Features

  • Micro-framework: Minimal core with extensions for additional functionality
  • Flexible: No assumptions about database, templating engine, or other components
  • Mature ecosystem: Thousands of extensions available
  • Simple routing: Decorator-based URL routing
  • Built-in development server: Easy testing and debugging

Installation

1

pip install Flask

Quick Start

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from flask import Flask

app = Flask(__name__)

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

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

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

Building APIs with Flask

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from flask import Flask, jsonify, request

app = Flask(__name__)

# Sample data
users = [
    {'id': 1, 'name': 'John Doe', 'email': '[email protected]'},
    {'id': 2, 'name': 'Jane Smith', 'email': '[email protected]'}
]

@app.route('/api/users', methods=['GET'])
def get_users():
    return jsonify(users)

@app.route('/api/users', methods=['POST'])
def create_user():
    data = request.get_json()
    new_user = {
        'id': len(users) + 1,
        'name': data['name'],
        'email': data['email']
    }
    users.append(new_user)
    return jsonify(new_user), 201

@app.route('/api/users/<int:user_id>', methods=['GET'])
def get_user(user_id):
    user = next((u for u in users if u['id'] == user_id), None)
    if user:
        return jsonify(user)
    return jsonify({'error': 'User not found'}), 404

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

Flask vs FastAPI Comparison

Feature Flask FastAPI
Performance Moderate High (async)
Learning Curve Easy Moderate
Type Hints Manual Built-in
API Documentation Manual (Flask-RESTX) Automatic
Async Support Limited (Flask 2.0+) Native
Ecosystem Very Large Growing
Data Validation Manual/Extensions Built-in (Pydantic)

Flask-SQLAlchemy

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from flask import Flask
from flask_sqlalchemy import SQLAlchemy

app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///example.db'
db = SQLAlchemy(app)

class User(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    username = db.Column(db.String(80), unique=True, nullable=False)
    email = db.Column(db.String(120), unique=True, nullable=False)

    def __repr__(self):
        return f'<User {self.username}>'

Flask-RESTful

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from flask import Flask
from flask_restful import Api, Resource

app = Flask(__name__)
api = Api(app)

class UserAPI(Resource):
    def get(self, user_id):
        # Get user logic
        return {'user_id': user_id}
    
    def put(self, user_id):
        # Update user logic
        return {'message': 'User updated'}
    
    def delete(self, user_id):
        # Delete user logic
        return {'message': 'User deleted'}

api.add_resource(UserAPI, '/api/users/<int:user_id>')

Flask-Login

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from flask import Flask
from flask_login import LoginManager, UserMixin, login_required

app = Flask(__name__)
app.secret_key = 'your-secret-key'
login_manager = LoginManager()
login_manager.init_app(app)

class User(UserMixin):
    def __init__(self, id):
        self.id = id

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

@app.route('/protected')
@login_required
def protected():
    return 'This is a protected route!'

When to Choose Flask

Choose Flask if you:

  • Need a simple, lightweight framework
  • Are building traditional web applications with templates
  • Want maximum flexibility in architecture choices
  • Are prototyping or building small applications
  • Prefer explicit over implicit (Zen of Python)
  • Need extensive customization options

Choose FastAPI if you:

  • Need high performance and async support
  • Want automatic API documentation
  • Prefer built-in data validation and serialization
  • Are building modern APIs or microservices
  • Want type safety and better IDE support

Migration from Flask to FastAPI

If you’re considering migrating from Flask to FastAPI:

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# Flask
from flask import Flask, jsonify, request

app = Flask(__name__)

@app.route('/users', methods=['POST'])
def create_user():
    data = request.get_json()
    # Manual validation needed
    return jsonify({'id': 1, 'name': data['name']})

# FastAPI equivalent
from fastapi import FastAPI
from pydantic import BaseModel

app = FastAPI()

class User(BaseModel):
    name: str
    email: str

@app.post('/users')
async def create_user(user: User):
    # Automatic validation
    return {'id': 1, 'name': user.name}

Resources

Comparison with Core Stack

View all alternatives →
#python #web-framework #api #micro-framework