FastAPI is a modern, high-performance web framework for building APIs with Python. It's designed to be fast, easy to use, and leverages Python type hints for automatic validation and documentation generation. FastAPI is built on top of Starlette for web parts and Pydantic for data validation.
FastAPI is built on three core technologies. ASGI provides asynchronous server gateway interface for handling many concurrent requests. Starlette serves as the lightweight web framework foundation. Pydantic handles data validation and serialization using Python type hints. These technologies work together to make FastAPI both fast and developer-friendly.
Here's a basic FastAPI example. First, we import FastAPI from the fastapi module. Then we create an app instance. We define a route using the app.get decorator, specifying the path. Finally, we define a function that returns a dictionary, which FastAPI automatically converts to JSON. This simple example shows how FastAPI uses decorators and type hints to create web APIs.
Let's see how FastAPI processes requests. First, a client sends an HTTP request. The ASGI server receives this request and passes it to FastAPI. FastAPI's router matches the request to the appropriate handler function. Pydantic validates the incoming data based on type hints. The handler function executes and returns data. Finally, FastAPI serializes the response and sends it back through the ASGI server to the client.
FastAPI offers many key benefits that make it an excellent choice for building APIs. It provides high performance comparable to NodeJS and Go. It automatically generates interactive API documentation using OpenAPI standards. Type safety is built-in through Python type hints. Async and await support makes it perfect for handling concurrent requests. Data validation happens automatically with Pydantic. And it's production-ready with excellent tooling support. FastAPI combines modern Python features with high performance and ease of use.