Assume I have this code:

class Spam:
    def eggs(__some_kwarg:int=None):
        print(__some_kwarg)

I can call Spam.bar with keyword arguments as expected from mangling:

>>> Spam.eggs(10)
10
>>> Spam.eggs(_Spam__some_kwarg=10)
10

However, in the __annotations__ field, the argument name is not mangled:

>>> Spam.eggs.__annotations__
{'__some_kwarg': <class 'int'>}

This is an inconsistency which makes it difficult to work with function annotations in this case.