Things to check first

• I have searched the existing issues and didn't find my bug already reported there

• I have checked that my bug is still present in the latest release

Typeguard version

4.3.0

Python version

Python 3.10.4

What happened?

Expected typeguard to ignore private attributes of the typing_extension.Protocol so that type checking would pass.

Note: Honestly this was my first intuition, but I realize it might be out of scope as I'm not sure what your stance is with respect to supporting the typing_extensions package. Perhaps this issue is more a feature request to allow configuring custom attributes that typeguard will ignore when typechecking protocols.

How can we reproduce the bug?

import typing_extensions
import builtins
import typeguard

class IDo(typing_extensions.Protocol):
    def do_something(self) -> builtins.str:
        ...

def doer(do: IDo) -> builtins.str:
    typeguard.check_type(value=do, expected_type=IDo)
    return do.do_something()

class DefaultDo:
    def do_something(self) -> builtins.str:
        return "did something"
    
print(doer(DefaultDo()))

Running the above program will result in:

typeguard.TypeCheckError: __main__.DefaultDo is not compatible with the IDo protocol because it has no attribute named '__protocol_attrs__'

Indeed, extending the typing_extensions.Protocol adds the __protocol_attrs__ attribute and causes the mismatch. I did notice however that typeguard has provisions to ignore private attributes of the typing.Protocol class:

So I was thinking this might be extended to support typing_extension.Protocol? If not, it would be great if we had some way to inject custom attributes we'd like typeguard to ignore.