Why FastAPI exists

Introduction

FastAPI exists to help developers build web APIs quickly and easily with automatic validation and great performance.

When you want to create a web service that responds to requests fast.

When you need automatic checks to make sure data sent to your API is correct.

When you want to write less code but get more features like documentation automatically.

When you want your API to handle many users at the same time without slowing down.

When you want to use modern Python features to write clean and clear code.

Syntax

FastAPI

from fastapi import FastAPI

app = FastAPI()

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

FastAPI uses Python functions decorated with route paths like @app.get("/") to define API endpoints.

It supports async functions for better performance with many users.

Examples

This example shows how to get a path parameter and return it in the response.

FastAPI

from fastapi import FastAPI

app = FastAPI()

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

This example shows how FastAPI automatically checks the data sent to the API using a model.

FastAPI

from fastapi import FastAPI
from pydantic import BaseModel

app = FastAPI()

class Item(BaseModel):
    name: str
    price: float

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

Sample Program

This simple FastAPI app returns a welcome message when you visit the root URL.

FastAPI

from fastapi import FastAPI

app = FastAPI()

@app.get("/")
async def read_root():
    return {"message": "Welcome to FastAPI!"}

Important Notes

FastAPI automatically creates interactive API docs you can try in your browser.

It uses Python type hints to check data and generate docs.

Summary

FastAPI helps build fast and easy web APIs.

It checks data automatically and creates docs for you.

It uses modern Python features for clean code and good performance.