10.3.1 Using Flask or FastAPI for basic API development

Both Flask and FastAPI are popular Python frameworks used for building APIs. Each of these frameworks has its own strengths, and your choice may depend on your project’s requirements, performance needs, and personal preference. Below is a comparison of both frameworks, followed by examples of building a basic API using each.

1. Flask

Flask is a micro-framework that is lightweight and flexible, suitable for small to medium-sized applications. It is one of the oldest and most widely used Python frameworks for web development.

Advantages of Flask:

• Simple and Minimalistic: Flask does not impose a lot of restrictions, allowing you to structure your application as you see fit.
• Large Ecosystem: A wide variety of libraries and extensions are available for different tasks (e.g., authentication, database handling, etc.).
• Good Documentation: Flask has excellent documentation and a large community for support.

Example of Basic API with Flask

1. Install Flask:

   pip install Flask
   

2. Create a simple Flask API:

   from flask import Flask, jsonify, request
   
   app = Flask(__name__)
   
   users = [{"id": 1, "name": "Alice"}, {"id": 2, "name": "Bob"}]
   
   @app.route('/api/users', methods=['GET'])
   def get_users():
       return jsonify(users)
   
   @app.route('/api/users', methods=['POST'])
   def add_user():
       user_data = request.get_json()
       users.append(user_data)
       return jsonify({"message": "User added successfully"}), 201
   
   if __name__ == '__main__':
       app.run(debug=True)
   

   Explanation:
   • The @app.route decorator defines routes for the API. GET /api/users returns a list of users, and POST /api/users allows adding a new user.
   • The request.get_json() method extracts the data from a POST request.
   • The API runs on localhost:5000 by default.
3. Running the Flask app:

   python app.py
   

   You can now test your API using a tool like Postman or curl.

2. FastAPI

FastAPI is a modern, high-performance web framework for building APIs with Python 3.7+ based on standard Python type hints. It is designed to be faster and more feature-rich than Flask, especially for building APIs with asynchronous capabilities.

Advantages of FastAPI:

• Faster: It is one of the fastest Python frameworks available, thanks to asynchronous programming and automatic optimization for performance.
• Automatic Validation and Documentation: FastAPI automatically validates data and generates API documentation using Swagger and ReDoc.
• Type Hints Support: Built on Python's type hints, FastAPI provides better editor support, error checking, and automatic generation of request validation.
• Asynchronous Support: FastAPI natively supports asynchronous endpoints, making it suitable for high-concurrency applications.

Example of Basic API with FastAPI

1. Install FastAPI and Uvicorn (Uvicorn is an ASGI server to run FastAPI applications):

   pip install fastapi uvicorn
   

2. Create a simple FastAPI app:

   from fastapi import FastAPI
   from pydantic import BaseModel
   
   app = FastAPI()
   
   # Pydantic model for user
   class User(BaseModel):
       id: int
       name: str
   
   users = [{"id": 1, "name": "Alice"}, {"id": 2, "name": "Bob"}]
   
   @app.get("/api/users")
   def get_users():
       return users
   
   @app.post("/api/users")
   def add_user(user: User):
       users.append(user.dict())
       return {"message": "User added successfully"}
   
   

   Explanation:
   • FastAPI uses Pydantic models (e.g., User) for request data validation and serialization. Pydantic validates the incoming data automatically based on the defined types.
   • The @app.get and @app.post decorators are used to define the API routes.
   • FastAPI automatically validates the incoming request and generates error responses if the data doesn’t match the specified format.
3. Running the FastAPI app:

   uvicorn app:app --reload
   

   The application will run at http://127.0.0.1:8000.
   • Automatic Swagger UI: Visit http://127.0.0.1:8000/docs to see automatically generated API documentation.
   • ReDoc UI: Visit http://127.0.0.1:8000/redoc for an alternative documentation view.

Key Differences Between Flask and FastAPI

When to Use Flask vs. FastAPI

• Flask is a great choice if:
  • You’re building simple, small-scale APIs.
  • You need flexibility in structuring the application.
  • You’re already familiar with Flask’s ecosystem and have a large number of libraries available.
• FastAPI is a better choice if:
  • You need high performance, especially for handling many concurrent requests.
  • You want automatic data validation and API documentation.
  • You’re working with asynchronous APIs or need more advanced features like automatic API documentation.
  • You want better support for type checking, which improves code quality and editor support.

Conclusion

Both Flask and FastAPI are powerful tools for building APIs in Python. Flask is a great choice for simpler applications or if you want more control over the design of your API. On the other hand, FastAPI offers better performance and modern features like data validation and automatic documentation, making it ideal for larger and more complex APIs.

Choose the framework that best fits your needs based on your project’s requirements and your comfort with asynchronous programming and data validation.