python-fastapi

Python FastAPI

Overview

FastAPI is a modern, high-performance Python web framework for building APIs. It uses Python type hints for automatic validation, serialization, and OpenAPI documentation.

Project Structure

src/
├── main.py                  # FastAPI app instance + startup
├── config.py                # Settings via pydantic-settings
├── routers/
│   ├── auth.py              # Auth endpoints
│   └── users.py             # User endpoints
├── models/
│   ├── user.py              # SQLAlchemy / ORM models
│   └── schemas.py           # Pydantic request/response schemas
├── services/
│   └── user_service.py      # Business logic
├── middleware/
│   └── auth.py              # Auth dependency
├── db/
│   ├── session.py           # Database session
│   └── migrations/          # Alembic migrations
└── tests/
    ├── conftest.py           # Fixtures
    └── test_users.py

Core Patterns

App Setup

from fastapi import FastAPI
from contextlib import asynccontextmanager

@asynccontextmanager
async def lifespan(app: FastAPI):
    # Startup
    await db.connect()
    yield
    # Shutdown
    await db.disconnect()

app = FastAPI(title="My API", lifespan=lifespan)
app.include_router(auth_router, prefix="/auth", tags=["auth"])
app.include_router(users_router, prefix="/users", tags=["users"])

Pydantic Schemas

from pydantic import BaseModel, EmailStr, Field

class UserCreate(BaseModel):
    email: EmailStr
    password: str = Field(min_length=8)
    name: str = Field(max_length=100)

class UserResponse(BaseModel):
    id: int
    email: str
    name: str

    model_config = {"from_attributes": True}  # ORM mode

Dependency Injection

from fastapi import Depends, HTTPException, status
from fastapi.security import OAuth2PasswordBearer

oauth2_scheme = OAuth2PasswordBearer(tokenUrl="/auth/token")

async def get_current_user(token: str = Depends(oauth2_scheme)) -> User:
    payload = decode_jwt(token)
    if not payload:
        raise HTTPException(status_code=status.HTTP_401_UNAUTHORIZED)
    user = await user_service.get_by_id(payload["sub"])
    if not user:
        raise HTTPException(status_code=status.HTTP_404_NOT_FOUND)
    return user

# Use in endpoint
@router.get("/me", response_model=UserResponse)
async def get_me(user: User = Depends(get_current_user)):
    return user