FastAPI Helper
Build modern, high-performance Python APIs with FastAPI.
Quick Start
python
from fastapi import FastAPI
app = FastAPI()
@app.get("/")
async def root():
return {"message": "Hello World"}
Run: uvicorn main:app --reload
Core Concepts
Route Decorators
| Decorator | HTTP Method |
|---|---|
@app.get() | GET |
@app.post() | POST |
@app.put() | PUT |
@app.delete() | DELETE |
@app.patch() | PATCH |
Parameter Functions
| Function | Source |
|---|---|
Path() | URL path /items/{id} |
Query() | Query string ?q=foo |
Body() | JSON body |
Header() | HTTP headers |
Cookie() | Cookies |
Form() | Form data |
File() / UploadFile | File uploads |
Dependency Injection
python
from fastapi import Depends
async def get_db():
db = SessionLocal()
try:
yield db
finally:
db.close()
@app.get("/items/")
async def read_items(db: Session = Depends(get_db)):
return db.query(Item).all()
Common Imports
python
from fastapi import (
FastAPI, APIRouter, Depends, HTTPException, status,
Request, Response, BackgroundTasks, WebSocket,
Path, Query, Body, Header, Cookie, Form, File, UploadFile
)
from fastapi.responses import JSONResponse, HTMLResponse, FileResponse, RedirectResponse
from fastapi.middleware.cors import CORSMiddleware
from pydantic import BaseModel, Field, EmailStr
Reference Documentation
Load these based on task:
| Task | Reference File |
|---|---|
| Routes, APIRouter, decorators | references/routing.md |
| Path, Query, Body, Form, File params | references/parameters.md |
| Response types, status codes, headers | references/responses.md |
| Depends, Security, OAuth2 | references/dependencies.md |
| Middleware, CORS, lifespan, BackgroundTasks | references/middleware-events.md |
| WebSocket connections | references/websockets.md |
| HTTPException, error handlers | references/exceptions.md |
| Pydantic models, validation | references/pydantic-models.md |
| TestClient, pytest fixtures | references/testing.md |
Common Patterns
CRUD Endpoint Structure
python
from fastapi import APIRouter, Depends, HTTPException, status
from sqlalchemy.orm import Session
router = APIRouter(prefix="/items", tags=["items"])
@router.get("/", response_model=list[ItemOut])
async def list_items(skip: int = 0, limit: int = 100, db: Session = Depends(get_db)):
return db.query(Item).offset(skip).limit(limit).all()
@router.get("/{item_id}", response_model=ItemOut)
async def get_item(item_id: int, db: Session = Depends(get_db)):
item = db.query(Item).filter(Item.id == item_id).first()
if not item:
raise HTTPException(status_code=404, detail="Item not found")
return item
@router.post("/", response_model=ItemOut, status_code=status.HTTP_201_CREATED)
async def create_item(item: ItemCreate, db: Session = Depends(get_db)):
db_item = Item(**item.model_dump())
db.add(db_item)
db.commit()
db.refresh(db_item)
return db_item
@router.put("/{item_id}", response_model=ItemOut)
async def update_item(item_id: int, item: ItemUpdate, db: Session = Depends(get_db)):
db_item = db.query(Item).filter(Item.id == item_id).first()
if not db_item:
raise HTTPException(status_code=404, detail="Item not found")
for key, value in item.model_dump(exclude_unset=True).items():
setattr(db_item, key, value)
db.commit()
return db_item
@router.delete("/{item_id}", status_code=status.HTTP_204_NO_CONTENT)
async def delete_item(item_id: int, db: Session = Depends(get_db)):
db_item = db.query(Item).filter(Item.id == item_id).first()
if not db_item:
raise HTTPException(status_code=404, detail="Item not found")
db.delete(db_item)
db.commit()
CORS Setup
python
from fastapi.middleware.cors import CORSMiddleware
app.add_middleware(
CORSMiddleware,
allow_origins=["http://localhost:3000"],
allow_credentials=True,
allow_methods=["*"],
allow_headers=["*"],
)
JWT Authentication Pattern
python
from fastapi import Depends, HTTPException, status
from fastapi.security import OAuth2PasswordBearer
oauth2_scheme = OAuth2PasswordBearer(tokenUrl="token")
async def get_current_user(token: str = Depends(oauth2_scheme)):
user = decode_token(token)
if not user:
raise HTTPException(
status_code=status.HTTP_401_UNAUTHORIZED,
detail="Invalid credentials",
headers={"WWW-Authenticate": "Bearer"},
)
return user
@app.get("/users/me")
async def read_users_me(current_user: User = Depends(get_current_user)):
return current_user