Bug report

Bug description:

I'm playing around with PEP 649, PEP 749 annotations and I found this surprising behaviour:

class C:
    x: str
    def __annotate__(format):
        if format != 1:
            raise NotImplementedError()
        return {'x': int}

assert C.__annotate__(1) == {'x': int} # This returns {'x': str} and fails

I'm not yet sure why I would write code with annotations and then also write an explicit __annotate__, but I would expect the explicit method to prevail over the compiler-generated one. If I explicitly set C.__annotate__ = some_func afterwards it works as I would expect.

Calling dis on the provided example shows both __annotate__s getting compiled, and one overwriting the other in the class.

Related to #119180.

CPython versions tested on:

3.14, CPython main branch

Operating systems tested on:

Linux

Linked PRs

• gh-133037: Add test for shadowing __annotate__ #133084