Like many static analyzers in ambiguous situations, you have to decide whether the possibility of false positives is worth the safety. In this case I'd flag it knowing that it could be marked ignored as needed (same with open() if it was used).

I have toyed with a MyPy plugin to do this, but the arbitrary state storage/cache is a bit limited to do good call graph and function coloring (metadata can be on types but not functions). And there's just not many other good _extensible_ static analysis libraries. Language like Go have static analysis libraries that let you store/cache arbitrary state/facts on all constructs.