FastAPI Python Library CheatSheet

FastAPI is a modern, fast (high-performance), web framework for building APIs with Python 3.7+ based on standard Python type hints. It is designed to be easy to use and efficient, making it a popular choice among developers for building robust and scalable APIs. To help you harness the power of FastAPI more effectively, here’s a cheatsheet that covers some of the essential concepts and features.

Installation

pip install fastapi

Creating a FastAPI Application

from fastapi import FastAPI

app = FastAPI()

Define Endpoints

from fastapi import FastAPI

app = FastAPI()

@app.get("/")
def read_root():
    return {"Hello": "World"}

@app.get("/items/{item_id}")
def read_item(item_id: int, query_param: str = None):
    return {"item_id": item_id, "query_param": query_param}

Request Parameters

Query Parameters

from fastapi import FastAPI

app = FastAPI()

@app.get("/items/")
def read_item(skip: int = 0, limit: int = 10):
    return {"skip": skip, "limit": limit}

Path Parameters

from fastapi import FastAPI

app = FastAPI()

@app.get("/items/{item_id}")
def read_item(item_id: int, q: str = None):
    return {"item_id": item_id, "q": q}

Request Body

from fastapi import FastAPI, Body

app = FastAPI()

@app.post("/items/")
def create_item(item: dict = Body(...)):
    return {"item": item}

Query Parameters and Types

from fastapi import FastAPI, Query

app = FastAPI()

@app.get("/items/")
def read_item(skip: int = Query(0, title="Skip", description="Number of items to skip")):
    return {"skip": skip}

Path Parameters and Types

from fastapi import FastAPI, Path

app = FastAPI()

@app.get("/items/{item_id}")
def read_item(item_id: int = Path(..., title="Item ID", description="The ID of the item")):
    return {"item_id": item_id}

Request Body and Types

from fastapi import FastAPI, Body

app = FastAPI()

class Item:
    name: str
    description: str = None
    price: float
    tax: float = None

@app.post("/items/")
def create_item(item: Item):
    return {"item": item}

Request Headers

from fastapi import FastAPI, Header

app = FastAPI()

@app.get("/items/")
def read_item(api_key: str = Header(..., convert_underscores=False)):
    return {"api_key": api_key}

Dependency Injection

from fastapi import FastAPI, Depends

app = FastAPI()

async def get_db():
    db = DBSession()
    try:
        yield db
    finally:
        db.close()

@app.get("/items/")
async def read_items(db: Session = Depends(get_db)):
    return db.query(Item).all()

OAuth2 Authentication

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

app = FastAPI()

oauth2_scheme = OAuth2PasswordBearer(tokenUrl="token")

@app.get("/items/")
def read_items(token: str = Depends(oauth2_scheme)):
    return {"token": token}

Middleware

from fastapi import FastAPI, Request

app = FastAPI()

async def simple_middleware(request: Request, call_next):
    print("Middleware Before Request")
    response = await call_next(request)
    print("Middleware After Request")
    return response

app.middleware(simple_middleware)

@app.get("/")
def read_root():
    return {"Hello": "World"}

This cheatsheet covers some of the key features and concepts of FastAPI. For more detailed information, refer to the official documentation. Use this cheatsheet as a quick reference guide to accelerate your development process with FastAPI.

FAQ