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

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

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"