fastapi cannot run in python 3.12

[zhugezifang]

fastapi cannot run in python 3.12

[peterdresslar]

A workaround is to add the Pipfile as suggested here:

https://vercel.com/docs/functions/runtimes/python#python-version

...setting python_version = "3.9" ... and note that you may be able to just run your fastapi app normally without anything else special like a vercel.json file. As of now, seems to work fine with Node 20.x.

Note that the official example here:

https://github.com/digitros/nextjs-fastapi/

...somewhat buries the issue by including a 3.9.pyc file that apparently controls Vercel's selection of version during build. Unfortunately, this obfuscates the issue, somewhat violates the convention in the docs linked above, and anyway including /__python__ in the checked in files seems unusual.

Here's an example of nextjs, fastapi, and postgres working with Pipfile:

https://github.com/peterdresslar/fullstack-nextjs-fastapi-postgres

It deploys and works as-is; if python_version is incremented to 3.12, the build succeeds but the API itself 404s.

UPDATE:

Downgrading to 3.9, deploying, then upgrading the Pipfile to 3.12 and re-deploying, makes the example work now. Slowly, I'd point out, but it works. 🤷‍♂️