FastAPI

The FastAPI package is supported in Python Workers.

FastAPI applications use a protocol called the Asynchronous Server Gateway Interface (ASGI) ↗. This means that FastAPI never reads from or writes to a socket itself. An ASGI application expects to be hooked up to an ASGI server, typically uvicorn ↗. The ASGI server handles all of the raw sockets on the application’s behalf.

The Workers runtime provides an ASGI server ↗ directly to your Python Worker, which lets you use FastAPI in Python Workers.

Get Started

Python Workers are in beta. Packages do not run in production.

Currently, you can only deploy Python Workers that use the standard library. Packages cannot be deployed and will only work in local development for the time being.

Clone the cloudflare/python-workers-examples repository and run the FastAPI example:

git clone https://github.com/cloudflare/python-workers-examples
cd python-workers-examples/03-fastapi
npx wrangler@latest dev

Example code

from fastapi import FastAPI, Request
from pydantic import BaseModel

async def on_fetch(request, env):
    import asgi

    return await asgi.fetch(app, request, env)

app = FastAPI()

@app.get("/")
async def root():
    return {"message": "Hello, World!"}

@app.get("/env")
async def root(req: Request):
    env = req.scope["env"]
    return {"message": "Here is an example of getting an environment variable: " + env.MESSAGE}

class Item(BaseModel):
    name: str
    description: str | None = None
    price: float
    tax: float | None = None

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

@app.put("/items/{item_id}")
async def create_item(item_id: int, item: Item, q: str | None = None):
    result = {"item_id": item_id, **item.dict()}
    if q:
        result.update({"q": q})
    return result

@app.get("/items/{item_id}")
async def read_item(item_id: int):
    return {"item_id": item_id}