Astroid 2.0.1 Regression: Metaclass call no longer understood.

[kayhayen]

Steps to reproduce

class NodeCheckMetaClass(ABCMeta):
    kinds = {}

    # This is in conflict with either PyDev or Pylint 1.9.2 used fo Python2, it
    # should be "mcs" for one and "cls" for the other.
    # pylint: disable=I0021,bad-mcs-classmethod-argument

    def __new__(cls, name, bases, dictionary): # pylint: disable=I0021,arguments-differ
        _checkBases(name, bases)

        if "__slots__" not in dictionary:
            dictionary["__slots__"] = ()

        if "named_child" in dictionary:
            dictionary["__slots__"] += (intern("subnode_" + dictionary["named_child"]),)

        # Not a method:
        if "checker" in dictionary:
            dictionary["checker"] = staticmethod(dictionary["checker"])

        return ABCMeta.__new__(cls, name, bases, dictionary)

Current behavior

Warning is given:
nuitka/nodes/NodeMetaClasses.py:66 E1121 too-many-function-args
NodeCheckMetaClass.new Too many positional arguments for
classmethod call

Expected behavior

I would be really surprised if that new call got too many arguments for real. I expect no warning to be given of course. Maybe it has to do with bad-mcs-classmethod-argument which seemed to no longer be an issue with 2.0.0, which I currently do not use due to lack of Python3 support for 2.0.1

pylint --version output

python3.6 -m pylint --version
main.py 2.0.0
astroid 2.0.1
Python 3.6.3 (default, Mar 27 2018, 00:29:24)
[GCC 6.3.0 20170516]

[PCManticore]

Hi @kayhayen Thanks for the report! Can you also add in the description how the call site looks like for that error you are getting? It seems it involves the __new__ method of NodeCheckMetaClass but having how the call site looks like will help us debug this further.

[kayhayen]

I am not sure what you mean, with call site, I am not calling "new" myself.

I do something unusual with the metaclass afterwards:

# For Python2/3 compatible source, we create a base class that has the metaclass
# used and doesn't require making a syntax choice.
NodeMetaClassBase = NodeCheckMetaClass(
    "NodeMetaClassBase",
    (object,),
    {
        "__slots__" : ()
    }
)

[PCManticore]

Yes, that's what I was interested in, thanks.

[cdeil]

I get a similar error when subclassing this class:

https://github.com/astropy/astropy/blob/ba8f644694d77865f7ba1376e7f0447fec5929b6/astropy/units/quantity.py#L196

With this example:

from astropy.units import Quantity


class Energy(Quantity):
    def __new__(cls, energy, unit=None, dtype=None, copy=True):
        self = super(Energy, cls).__new__(cls, energy, unit, dtype=dtype, copy=copy)
        return self

I get this error:

$ pylint -E test.py
************* Module test
test.py:6:15: E1124: Argument 'dtype' passed by position and keyword in classmethod call (redundant-keyword-arg)

The error makes no sense to me, on that line I pass dtype=dtype and it's not passed by position.

This is with astroid and pylint master from today.

$ pylint --version
pylint 2.2.0
astroid 2.0.4
Python 3.6.0 | packaged by conda-forge | (default, Feb 10 2017, 07:08:35) 
[GCC 4.2.1 Compatible Apple LLVM 7.3.0 (clang-703.0.31)]

If it's useful for you to have this in a separate issue, let me know and I'll copy this comment there.

[PCManticore]

Thanks @cdeil ! Let's move this to a separate issue, it seems related but a bit different at the same time that it should be on its own.

[cdeil]

OK, I've opened #2441 .