Bug report

Bug description:

According to the Python docs, annotate functions need to be actual functions. However, the C code doesn't enforce this, it enforces (using PyCallable_Check()) that the annotate 'function' is any callable:

This initially seems fine, but leads to some weird bugs.

class C:
  def __call__(self, format, /):
    if format > 2:
      raise NotImplementedError
    return {'x': int}

def f(x): ...
f.__annotate__ = C()

from annotationlib import get_annotations, Format
get_annotations(f, format=Format.STRING) # AttributeError: 'C' object has no attribute '__closure__' ...

And similar for get_annotations(f, format=Format.FORWARDREF), trying to find the annotation function's __builtins__, which only exists on functions (not arbitrary callables).

I'm happy to make a PR to replace the PyCallable_Check() with PyFunction_Check() in the relevant C code for setting __annotate__, but I guess this might be a breaking change? I'm not sure, so I thought I'd check first before making it. The other option would be checking for the presence of __closure__/__builtins__/etc. before accessing them in annotationlib.

CPython versions tested on:

CPython main branch

Operating systems tested on:

Linux