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Example Code

from fastapi import APIRouter, FastAPI

app = FastAPI()
api = APIRouter(prefix="/api")

@api.post("/foobar")
def foobar():
    return {"foo": "bar"}

# I made a typo where I should have written `app.include_router(api)`.
api.include_router(api)

Description

Because of the circular reference caused by api.include_router(api), it is desirable for FastAPI to promptly raise an error and terminate.

However, when executing this code, it becomes impossible to exit the infinite loop that uvicorn falls into.

Operating System

macOS

Operating System Details

No response

FastAPI Version

0.110.1

Pydantic Version

2.6.4

Python Version

Python 3.12.2

Additional Context

If your server doesn't start in an infinite loop, there's a possibility that the phenomenon described in this discussion is occurring.