Q: will Mangum run lifespan multiple times?

[dimaqq]

I'm trying to run fastapi app with custom lifespan-aware middleware.
It works fine under uvicorn, but fails oddly under mangum.

The error is:

File "my-middleware-that-tries-to-honour-lifespan.py", line 98, in __call__
 await self.under.__aenter__()
File "/usr/local/lib/python3.10/contextlib.py", line 197, in __aenter__
 del self.args, self.kwds, self.func
AttributeError: args

(That's Py 3.10 error, the exception is a bit misleading: https://bugs.python.org/issue45996)

The cause is that my middleware accepts an instance of an asynccontextmanager, and it runs __aenter__ on lifespan.startup
and __aexit__ on lifespan.shutdown.

In the FastAPI/starlette/uvicorn combo, there's a case (maybe even an assumption) that startup and shutdown are ran only once. After that the entire app is thrown away.

However, it seems, as if mangum runs lifespan.startup multiple times.
Perhaps that's how it deals with lambda being suspended?

[jordaneremieff]

The startup and shutdown events are only expected to run once.

How are you running Mangum using 3.10? It currently only supports the latest Python version that AWS Lambda supports (3.9).

I’ll move this to discussions because it doesn’t seem like a bug specifically in Mangum at this point.