Pylint: Pylint gives a false positive when an override method changes the argument names

[marmistrz]

Steps to reproduce

Lint this code:

import json
class MyJsonEncoder(json.JSONEncoder):
    # pylint: disable=method-hidden
    # See https://github.com/PyCQA/pylint/issues/414 for reference
    def default(self, obj) -> str:
        return super().default(obj)

Current behavior

W:  5, 4: Parameters differ from overridden 'default' method (arguments-differ)

Expected behavior

No warning

pylint --version output

pylint 1.7.2, 
astroid 1.5.3
Python 3.6.2 (default, Jul 20 2017, 03:52:27) 
[GCC 7.1.1 20170630]

[sam-s]

Still present with

pylint 1.8.1, 
astroid 1.6.0
Python 2.7.14 (default, Sep 25 2017, 09:53:22) 
[GCC 4.2.1 Compatible Apple LLVM 9.0.0 (clang-900.0.37)]

[hiranya911]

Present with:

pylint 1.8.4, 
astroid 1.6.3
Python 2.7.12 (default, Dec  4 2017, 14:50:18) 
[GCC 5.4.0 20160609]

[PCManticore]

Hey folks! Just wanted to say that I'm aware that this bug hasn't been fixed yet.

[AWhetter]

Why do you consider this a false positive? Renaming arguments means that as a user I could no longer do something like

encoder = MyEncoder()
kwargs = {'o': to_encode}
encoder.default(**kwargs)

In my opinion, the message is correct and arguments should not be renamed.

[PCManticore]

Ashley is right here. I'm not sure why we argue that pylint is emitting incorrectly this message when technically it is correct, the parameter has a different name.

[marmistrz]

And encoder.default(o=to_encode) would cease to work too. Thanks :)

[nat-n]

I have another example of the original issue where I don't think it's so clear that pylint is justified in complaining.

Consider:

class A:
    def method_x(self, **kwargs: Any):
        pass

class B(A):
    def method_x(self, *, foo: Optional[Any] = None, **kwargs: Any):
        pass

I would argue that since the signature for B.method_X is subsumed by A.method_X; indeed the set of valid inputs for each is identical, it should be acceptable. However pylint 2.5.3 disagrees.