Python 101: Flask vs FastAPI

Flask vs FastAPI: A Detailed Comparison

Flask and FastAPI are two popular web frameworks used for building APIs and web applications in Python. Although they share similar purposes, they have distinct differences in terms of speed, usability, and functionality. Below, we’ll explore these differences using a structured comparison format.

1. Quick Answer

• Flask is a lightweight web framework that is simple, flexible, and widely used for its ease of use.
• FastAPI is a modern, high-performance web framework for building APIs with Python, based on standard Python type hints, and designed for speed and ease of use.

Which one to use?

• Choose Flask if you need a straightforward framework for small to medium-sized projects with fewer concurrency requirements.
• Choose FastAPI if you need a high-performance, async-ready framework with built-in data validation and type hinting.

2. 5Ws Analysis (Who, What, When, Where, Why)

Who uses Flask and FastAPI?

• Flask is widely used by developers and companies for small to medium web applications, microservices, and educational projects.
• FastAPI is often chosen by developers and companies looking for high-performance APIs with async support, real-time applications, or projects with complex data validation requirements.

What are Flask and FastAPI?

• Flask is a micro web framework written in Python, known for its simplicity and ease of integration with extensions.
• FastAPI is a modern web framework built on top of Starlette and Pydantic, offering automatic validation, data serialization, and high performance.

When to use Flask or FastAPI?

• Use Flask for projects that require a simple, easy-to-learn framework with synchronous request handling.
• Use FastAPI for high-performance applications, real-time APIs, or projects that require asynchronous programming.

Where are Flask and FastAPI used?

• Flask is commonly used in educational contexts, simple microservices, and internal tools.
• FastAPI is widely used in production environments for APIs, data processing, and machine learning backends.

Why choose Flask or FastAPI?

• Choose Flask for its simplicity, maturity, and large ecosystem of extensions.
• Choose FastAPI for its speed, automatic data validation, and ease of use with modern Python features.

3. Code Example

Flask Example

# app.py - A simple Flask example
from flask import Flask, jsonify

app = Flask(__name__)

@app.route('/')
def home():
    return jsonify(message="Hello from Flask")

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

FastAPI Example

# main.py - A simple FastAPI example
from fastapi import FastAPI

app = FastAPI()

@app.get("/")
def read_root():
    return {"message": "Hello from FastAPI"}

if __name__ == '__main__':
    import uvicorn
    uvicorn.run(app, host="127.0.0.1", port=8000)

4. Key Points & Tips

Tips:

• If you’re new to Python and web development, start with Flask to grasp the basics.
• If your application needs to handle many concurrent requests or uses WebSockets, choose FastAPI.
• Use Flask’s wide range of extensions like Flask-SQLAlchemy for easier integration with other tools.

5. Comparison Table

6. Interview Questions

1. When should you choose Flask over FastAPI for a project?

   • Answer: Choose Flask if you need a simple, flexible framework for small projects or microservices without high concurrency requirements.

2. How does FastAPI achieve higher performance compared to Flask?

   • Answer: FastAPI is built on ASGI (Asynchronous Server Gateway Interface) and uses asynchronous request handling, which improves performance and enables handling more concurrent connections.

3. What are the major limitations of Flask for building APIs?

   • Answer: Flask does not provide built-in validation, lacks async support, and requires additional libraries for API documentation and serialization.

4. Can you use Flask and FastAPI together in a project?

   • Answer: Yes, Flask and FastAPI can coexist, for example, using Flask for traditional web routes and FastAPI for handling high-performance async APIs.

7. Conclusion

• Flask is a great choice for beginners or projects that do not need complex request handling or data validation. It’s mature, well-supported, and has a wide range of extensions.
• FastAPI excels in building high-performance APIs with its async capabilities, built-in validation, and auto-generated documentation. It’s ideal for modern applications and real-time systems.

Final Recommendation:
Choose Flask for straightforward projects and FastAPI for high-performance, modern applications with complex data requirements.