Python's FastAPI vs Flask: A Deep Dive

Python has emerged as a dominant force in the world of web development, thanks to its versatility, readability, and extensive libraries. Two prominent frameworks that have gained significant popularity among Python developers are FastAPI and Flask. While both are used to create web applications and APIs, they have distinct approaches and cater to different needs.

Flask

Flask is a lightweight and flexible microframework that provides the essential building blocks for creating web applications. Its minimalist nature gives developers the freedom to customize and structure their applications as they see fit. Flask offers a simple and intuitive API, making it easy to learn and use.

FastAPI

FastAPI, on the other hand, is a modern, high-performance framework built on top of Starlette. It leverages advanced techniques like ASGI (Asynchronous Server Gateway Interface) and type hints to provide a fast, efficient, and developer-friendly experience. FastAPI offers features like automatic interactive API documentation, automatic data validation, and asynchronous support, making it a powerful choice for building modern, scalable web applications.

Key Differences:

Performance: FastAPI is generally considered faster than Flask, especially for asynchronous applications. Features: FastAPI offers more built-in features, such as automatic data validation, dependency injection, and OpenAPI documentation.

Learning Curve: Flask has a lower learning curve due to its simplicity, while FastAPI may require some additional learning for its more advanced features.

Use Cases: Flask is suitable for a wide range of applications, from small-scale projects to complex web applications. FastAPI is particularly well-suited for building high-performance APIs, microservices, and data-intensive applications.

Cheatsheet of Common FastAPI/Flask Commands:

FastAPI:

Creating a FastAPI application

from fastapi import FastAPI

app = FastAPI()        

Defining a route

@app.get("/")
def read_root():
    return {"Hello": "World"}        

Creating a path parameter

@app.get("/items/{item_id}")
def read_item(item_id: int):
    return {"item_id": item_id}        

Creating a query parameter

@app.get("/items/")
def read_item(skip: int = 0, limit: int = 10):
    return {"skip": skip, "limit": limit}        

Using both query and path parameters

@app.get("/users/{user_id}/items/{item_id}")
def read_user_item(
    user_id: int, item_id: int, q: str | None = None = None
):
    return {"user_id": user_id, "item_id": item_id, "q": q}        

Creating a new endpoint(eg: POST)

from fastapi import FastAPI, Body

app = FastAPI()

@app.post("/items/")
async def create_item(item: Item = Body(...)):
    return item        

Running the FastAPI app

if __name__ == "__main__":
    import uvicorn
    uvicorn.run(app, host="0.0.0.0", port=8000)        

Flask:

Creating a Flask app

from flask import Flask

app = Flask(__name__)        

Defining a route

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

Creating a path parameter

@app.route("/items/<int:item_id>")
def read_item(item_id):
    return {"item_id": item_id}        

Creating a query parameter

@app.route("/items/")
def read_item(skip=0, limit=10):
    return {"skip": skip, "limit": limit}        

Using query and path parameters

@app.route("/users/<int:user_id>/items/<int:item_id>")
def read_user_item(user_id, item_id, q=None):
    return {"user_id": user_id, "item_id": item_id, "q": q}        

Creating a new endpoint(eg: POST endpoint)

from flask import Flask, request, jsonify

app = Flask(__name__)

@app.route("/items/", methods=["POST"])
def create_item():
    item = request.get_json()
    return jsonify(item)        

Running the Flask app

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

Both FastAPI and Flask are powerful tools for building web applications and APIs in Python. The choice between them depends on the specific requirements of your project. If you need a high-performance, feature-rich framework with excellent documentation, FastAPI is an excellent choice. If you prefer a lightweight and flexible approach, Flask may be a better fit.I hope this article has provided you with a helpful overview of Pythons FastAPI and Flask. If you have any questions, please feel free to leave a comment below.