gh-124342: Wrap __annotate__ functions in functools.update_wrapper

[JelleZijlstra]

• Issue: PEP 649: functools.update_wrapper implementation #124342

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📚 Documentation preview 📚: https://cpython-previews--124346.org.readthedocs.build/

[vstinner]

LGTM.

I was just surprised that updating func.__annotations__ after update_wrapper(wrapper, func) doesn't update wrapper.__annotations__. Don't get me wrong, I'm fine with this behavior.

[vstinner]

Suggested change

	func = _get_get_annotations()
	return func(wrapped, format=format)
	get_annotations = _get_get_annotations()
	return get_annotations(wrapped, format=format)

[vstinner]

Another surprising behavior. I'm discovering __annotate__() so it's maybe by design, I don't know :-)

When I update annotations of the wrapped function, __annotate__() of the wrapped function doesn't change, whereas __annotate__() of the wrapper is updated.

$ ./python
>>> import functools
>>> def f(x: int = 1): return x
>>> def wrapper(*args): pass
>>> functools.update_wrapper(wrapper, f)
<function f at 0x7f19f44d3e90>

>>> f.__annotations__['x']
<class 'int'>
>>> import annotationlib
>>> f.__annotate__(annotationlib.Format.VALUE)
{'x': <class 'int'>}
>>> wrapper.__annotate__(annotationlib.Format.VALUE)
{'x': <class 'int'>}

>>> f.__annotations__['x'] = float
>>> f.__annotate__(annotationlib.Format.VALUE)  # <=== HERE
{'x': <class 'int'>}
>>> wrapper.__annotate__(annotationlib.Format.VALUE)  # <=== HERE
{'x': <class 'float'>}

I would expect getting the same value for both cases. Either <class 'int'> or <class 'float'>.

[vstinner]

cc @sobolevn

[JelleZijlstra]

This is because we use get_annotations, which always returns a fresh dictionary. Maybe I should change that.

[JelleZijlstra]

I made some changes to align with @ncoghlan's original proposal and @vstinner's feedback above, but I now think it's better to stick with what's currently on main. I'll write that up on the issue.