Fix __annotations__ being undefined

[Nickedude]

Fix annotations being undefined

Closes #10330

Using the variable __annotations__ currently leads to an error being raised incorrectly by mypy, as shown in the example in issue #10330:

print(__annotations__)

test.py:1: error: Name '__annotations__' is not defined
Found 1 error in 1 file (checked 1 source file)

This is because mypy can't find the definition of __annotations__. This PR adds a definition of __annotations__ to mypy, which means this type of error should not be raised anymore.

[Nickedude]

@JukkaL bump :)

[JukkaL]

Ah, there's a problem with test stubs.

[97littleleaf11]

lgtm!

[97littleleaf11]

@AlexWaygood @hauntsaninja Any suggestions on stub test failures?

[AlexWaygood]

Interesting! The teststubtest failures are (I think) because of this behaviour on Python <= 3.9 for modules which do not have any type annotations in their global namespace:

>>> import functools
>>> functools.__annotations__
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: module 'functools' has no attribute '__annotations__'

In Python >= 3.10, the behaviour is different: __annotations__ is always "present" (I think strictly speaking it's a descriptor, but let's leave that aside) in a module's global namespace, even if there are zero type annotations in that module's global namespace:

>>> import functools
>>> getattr(functools, "__annotations__")
{}
>>> hasattr(functools, "__annotations__")
True

So I'd probably say, in an ideal world:

• __annotations__ should always be added as an implicit module attribute if the Python version is >= 3.10.
• For Python < 3.10, it should probably only be added as an implicit module attribute if:
  • The module is being run as main; or,
  • The module has at least one type annotation in the global namespace.

But that sounds... complicated ://

[hauntsaninja]

I find https://docs.python.org/3/howto/annotations.html#annotations-howto to be a useful reference.

Leaving aside questions of how __annotations__ should work, if you just want stubtest to shut up, just add __annotations__ to here (make sure to add it above the TODO):

mypy/mypy/stubtest.py

Line 981 in c7a8162

"__path__", # mypy adds __path__ to packages, but C packages don't have it

[github-actions]

According to mypy_primer, this change has no effect on the checked open source code. 🤖🎉

[97littleleaf11]

if you just want stubtest to shut up

Yeah let's just follow other dunders.

[hauntsaninja]

Thanks for getting this over the line!

[KotlinIsland]

#4182