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 Python Workers provides an ASGI server ↗ that you can use directly in your Python Worker, which lets you use FastAPI in Python Workers.

Get Started

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
uv run pywrangler dev

Example code

from workers import WorkerEntrypoint
from fastapi import FastAPI, Request
from pydantic import BaseModel
import asgi

class Default(WorkerEntrypoint):
    async def fetch(self, request):
        return await asgi.fetch(app, request, self.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}