What is FastAPI?

What is FastAPI?

FastAPI is a modern, open-source Python web framework designed specifically for building APIs. It was created by Sebastián Ramírez in 2018 and has rapidly become one of the most popular Python frameworks in the world.

What makes FastAPI unique is its reliance on standard Python type hints. You declare the types of your data, and FastAPI handles validation, serialization, and documentation automatically.

Why Use FastAPI? (The Key Advantages)

• Extreme Performance: On par with Node.js and Go, thanks to its async-first design (ASGI).
• Automatic Docs: It generates interactive Swagger UI and ReDoc documentation at /docs and /redoc without any extra code.
• Type Safety: Uses Pydantic models to validate incoming data and serialize outgoing data.
• Async/Await Support: Native support for modern asynchronous Python.
• Standards-Based: Built on open standards like OpenAPI and JSON Schema.
• Great for AI/ML: The go-to choice for serving machine learning models.

FastAPI vs Django vs Flask

How FastAPI Works

FastAPI is built on two core libraries:

• Starlette: A lightweight ASGI framework for the web layer (routing, requests, responses).
• Pydantic: A data validation library for the data layer (type checking, serialization).

When you define a route, you also define the expected data types. FastAPI uses these types to validate incoming requests and format outgoing responses.

Getting Started with FastAPI

Here is how to create your first FastAPI app:

# Install FastAPI and Uvicorn
pip install fastapi uvicorn

# Create a file called main.py
from fastapi import FastAPI

app = FastAPI()

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

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

Run it with:

uvicorn main:app --reload

Visit http://127.0.0.1:8000/docs; to see the automatic interactive documentation.

When to Use FastAPI