fastapi

## What I do - Create REST APIs with FastAPI - Use Pydantic models for validation - Implement dependency injection - Handle async database operations - Create OpenAPI documentation - Implement authentication (OAuth2, JWT) - Use background tasks - Write pytest for FastAPI tests ## When to use me When building APIs with FastAPI. ## FastAPI Application ```python from fastapi import FastAPI, Depends, HTTPException, status from fastapi.security import OAuth2PasswordBearer, OAuth2PasswordRequestForm from typing import Annotated from pydantic import BaseModel, EmailStr from datetime import datetime, timedelta from jose import JWTError, jwt app = FastAPI( title="API", description="My FastAPI Application", version="1.0.0", docs_url="/docs", redoc_url="/redoc", ) SECRET_KEY = "your-secret-key" ALGORITHM = "HS256" ACCESS_TOKEN_EXPIRE_MINUTES = 30 oauth2_scheme = OAuth2PasswordBearer(tokenUrl="/api/v1/auth/token") class Token(BaseModel): access_token: str token_type: str class UserCreate(BaseModel): email: EmailStr password: str full_name: str | None = None class User(BaseModel): id: int email: EmailStr full_name: str | None is_active: bool = True created_at: datetime class UserResponse(BaseModel): id: int email: EmailStr full_name: str | None class Config: from_attributes = True @app.post("/api/v1/users", response_model=UserResponse, status_code=status.HTTP_201_CREATED) async def create_user(user: UserCreate, db: Session = Depends(get_db)) -> UserResponse: existing = db.query(User).filter(User.email == user.email).first() if existing: raise HTTPException( status_code=status.HTTP_400_BAD_REQUEST, detail="Email already registered", ) hashed_password = hash_password(user.password) db_user = User( email=user.email, full_name=user.full_name, hashed_password=hashed_password, ) db.add(db_user) db.commit() db.refresh(db_user) return UserResponse.model_validate(db_user) @app.post("/api/v1/auth/token") async def login( form_data: Annotated[OAuth2PasswordRequestForm, Depends()], db: Session = Depends(get_db), ) -> Token: user = authenticate_user(db, form_data.username, form_data.password) if not user: raise HTTPException( status_code=status.HTTP_401_UNAUTHORIZED, detail="Incorrect username or password", headers={"WWW-Authenticate": "Bearer"}, ) access_token_expires = timedelta(minutes=ACCESS_TOKEN_EXPIRE_MINUTES) access_token = create_access_token( data={"sub": user.email}, expires_delta=access_token_expires ) return Token(access_token=access_token, token_type="bearer") async def get_current_user( token: Annotated[str, Depends(oauth2_scheme)], db: Session = Depends(get_db), ) -> User: credentials_exception = HTTPException( status_code=status.HTTP_401_UNAUTHORIZED, detail="Could not validate credentials", headers={"WWW-Authenticate": "Bearer"}, ) try: payload = jwt.decode(token, SECRET_KEY, algorithms=[ALGORITHM]) email: str = payload.get("sub") if email is None: raise credentials_exception except JWTError: raise credentials_exception user = get_user_by_email(db, email=email) if user is None: raise credentials_exception return user @app.get("/api/v1/users/me") async def read_users_me( current_user: Annotated[User, Depends(get_current_user)], ) -> UserResponse: return UserResponse.model_validate(current_user) ``` ## Testing FastAPI ```python from fastapi.testclient import TestClient from sqlalchemy import create_engine from sqlalchemy.orm import sessionmaker @pytest.fixture def client(): app = create_app() return TestClient(app) @pytest.fixture def db_session(): engine = create_engine("sqlite:///./test.db") Session = sessionmaker(bind=engine) session = Session() yield session session.close() def test_create_user(client: TestClient): response = client.post( "/api/v1/users", json={"email": "test@example.com", "password": "secret123"}, ) assert response.status_code == status.HTTP_201_CREATED data = response.json() assert data["email"] == "test@example.com" assert "id" in data assert "password" not in data def test_login(client: TestClient): # First create user client.post( "/api/v1/users", json={"email": "test@example.com", "password": "secret123"}, ) # Then login response = client.post( "/api/v1/auth/token", data={"username": "test@example.com", "password": "secret123"}, ) assert response.status_code == 200 token = response.json() assert "access_token" in token assert token["token_type"] == "bearer" ```