Step-by-step articles on FastAPI, part of our Backend collection.
Showing 10 articles
FastAPI is a Python web framework built on type hints. You describe your inputs and outputs with types, and FastAPI validates requests, serialises responses and generates interactive API docs for you. Install and run pip install "fastapi[standard]" fastapi dev...
Pydantic models are the heart of FastAPI. Every field type and constraint becomes runtime validation and documentation. Field constraints from typing import Annotated from pydantic import BaseModel, EmailStr, Field class SignupRequest(BaseModel): email: EmailS...
FastAPI's Depends lets endpoints declare what they need (a database session, the current user, pagination settings) and FastAPI provides it. Dependencies can depend on other dependencies, and they're easy to replace in tests. A simple dependency from typing im...
SQLAlchemy 2.0 brought a cleaner, fully typed API and first-class async support. Combined with the asyncpg driver it's a solid choice for FastAPI apps. Install pip install "sqlalchemy[asyncio]" asyncpg alembic Engine and session # db.py from sqlalchemy.ext.asy...
This guide adds a /auth/token login endpoint that returns a JWT, and a dependency that protects routes. It follows the pattern FastAPI's own docs use. Install pip install pyjwt "pwdlib[argon2]" Hashing and tokens # security.py from datetime import datetime, ti...
FastAPI apps are easy to test because endpoints are plain functions behind an ASGI app, and dependencies can be swapped per test. A first test # test_books.py from fastapi.testclient import TestClient from main import app client = TestClient(app) def test_crea...
Two common needs in API servers: running code once when the app starts or stops, and doing a bit of work after the response is sent. Lifespan: startup and shutdown from contextlib import asynccontextmanager import httpx from fastapi import FastAPI @asynccontex...
Some responses shouldn't wait until everything is ready: large exports, progress updates, or text from an LLM. FastAPI's StreamingResponse sends data as your generator produces it. Streaming a large CSV from fastapi.responses import StreamingResponse @app.get(...
A production FastAPI deployment is usually a container running an ASGI server behind a reverse proxy or load balancer. Dockerfile FROM python:3.13-slim # uv for fast, reproducible installs COPY --from=ghcr.io/astral-sh/uv:latest /uv /usr/local/bin/uv WORKDIR /...
A single main.py is perfect for a prototype. As the API grows, split it by feature so each area of the product lives together. A feature-based layout app/ main.py # creates the app, includes routers config.py # settings from environment db.py # engine, session...
