This code:

async def f() -> None:
    pass
async def g() -> None:
    f()

is incorrect because f() isn't awaited. This will produce a runtime warning with the right debug settings, but mypy doesn't give any errors.

It would be nice if mypy could catch this, since I think it's a pretty common error in async code. This could be generalized to warning on other types or function return values that shouldn't be ignored (maybe open?), similar to __attribute__((warn_unused_result)) in GCC.