FastAPI: Building High-Performance REST APIs
Routing, path and query parameters, Pydantic validation, dependency injection, async databases, JWT authentication and Docker deployment — modern Python backend in one guide.
Getting Started
pip install fastapi "uvicorn[standard]"
# 热重载开发
uvicorn main:app --reload --port 8000from fastapi import FastAPI
app = FastAPI(title="Demo API")
@app.get("/")
async def root():
return {"message": "Hello, BackendWiki"}Open http://localhost:8000/docs and you already have interactive Swagger UI — FastAPI generates it from your type annotations.
Path, Query and Body with Pydantic
from pydantic import BaseModel, Field, EmailStr
from typing import Optional
class UserCreate(BaseModel):
name: str = Field(min_length=2, max_length=50)
email: EmailStr
age: Optional[int] = Field(default=None, ge=0, le=150)
@app.get("/users/{uid}")
async def get_user(uid: int): # 路径参数自动解析+类型校验
...
@app.get("/users")
async def list_users(
q: Optional[str] = None, # 查询参数
limit: int = 20, offset: int = 0,
):
...
@app.post("/users", status_code=201)
async def create_user(body: UserCreate):
return body # 响应也会序列化并校验Validation failures return HTTP 422 with detailed field-level errors automatically — no manual if-checking needed.
Dependency Injection
from fastapi import Depends
def get_db():
db = SessionLocal()
try:
yield db
finally:
db.close()
@app.get("/orders")
async def list_orders(db = Depends(get_db),
user = Depends(get_current_user)):
return db.query(Order).all()Dependencies are cached per request, support nested injection, and make testing easy — override get_db with a test session in fixtures.
JWT Authentication
from datetime import datetime, timedelta
import jwt
SECRET = "change-me"
def create_token(uid: int) -> str:
payload = {
"sub": uid,
"exp": datetime.utcnow() + timedelta(hours=2),
}
return jwt.encode(payload, SECRET, algorithm="HS256")
async def get_current_user(token: str = Depends(oauth2_scheme)):
try:
payload = jwt.decode(token, SECRET, algorithms=["HS256"])
return payload["sub"]
except jwt.PyJWTError:
raise HTTPException(401, "Invalid token")Packaging and Deployment
FROM python:3.12-slim
WORKDIR /app
COPY requirements.txt .
RUN pip install --no-cache-dir -r requirements.txt
COPY . .
EXPOSE 8000
CMD ["uvicorn", "main:app", "--host", "0.0.0.0", "--port", "8000"]Behind nginx or a container platform, run uvicorn with --workers 4 (or use gunicorn -k uvicorn.workers.UvicornWorker) to use multiple CPU cores.
快速开始
pip install fastapi "uvicorn[standard]"
# 热重载开发
uvicorn main:app --reload --port 8000from fastapi import FastAPI
app = FastAPI(title="Demo API")
@app.get("/")
async def root():
return {"message": "Hello, BackendWiki"}打开 http://localhost:8000/docs 就能看到交互式 Swagger 文档——FastAPI 根据类型注解自动生成。
路径、查询参数与 Pydantic 请求体
from pydantic import BaseModel, Field, EmailStr
from typing import Optional
class UserCreate(BaseModel):
name: str = Field(min_length=2, max_length=50)
email: EmailStr
age: Optional[int] = Field(default=None, ge=0, le=150)
@app.get("/users/{uid}")
async def get_user(uid: int): # 路径参数自动解析+类型校验
...
@app.get("/users")
async def list_users(
q: Optional[str] = None, # 查询参数
limit: int = 20, offset: int = 0,
):
...
@app.post("/users", status_code=201)
async def create_user(body: UserCreate):
return body # 响应也会序列化并校验校验失败自动返回 HTTP 422 并带逐字段错误详情，无需手写 if 校验。
依赖注入
from fastapi import Depends
def get_db():
db = SessionLocal()
try:
yield db
finally:
db.close()
@app.get("/orders")
async def list_orders(db = Depends(get_db),
user = Depends(get_current_user)):
return db.query(Order).all()依赖按请求缓存、支持嵌套注入，测试时在 fixture 里覆盖 get_db 即可替换为测试会话。
JWT 鉴权
from datetime import datetime, timedelta
import jwt
SECRET = "change-me"
def create_token(uid: int) -> str:
payload = {
"sub": uid,
"exp": datetime.utcnow() + timedelta(hours=2),
}
return jwt.encode(payload, SECRET, algorithm="HS256")
async def get_current_user(token: str = Depends(oauth2_scheme)):
try:
payload = jwt.decode(token, SECRET, algorithms=["HS256"])
return payload["sub"]
except jwt.PyJWTError:
raise HTTPException(401, "Invalid token")打包部署
FROM python:3.12-slim
WORKDIR /app
COPY requirements.txt .
RUN pip install --no-cache-dir -r requirements.txt
COPY . .
EXPOSE 8000
CMD ["uvicorn", "main:app", "--host", "0.0.0.0", "--port", "8000"]生产环境在 Nginx 或容器平台后用 uvicorn --workers 4（或 gunicorn -k uvicorn.workers.UvicornWorker）利用多核。