self.__class__() not supported

[timabbott]

Mypy is OK with accessing self.__class__ but not self.__class__(...)

Reproducer:

class S(object):
    def foo(self):
        return self.__class__()

Error:

/home/tabbott/foo.py: note: In member "foo" of class "S":
/home/tabbott/foo.py:4: error: "type" not callable

[gvanrossum]

Well, maybe there should be a better error message, but calling
self.class() to construct an instance is very problematic. A
subclass constructor might have a different signature that is
unknowable when you are checking the base class. So unless in your
world you have a strong rule that subclass constructors must conform
to a certain signature, this should be flagged IMO. (OTOH a way to
declare that you do have such a rule might be useful -- maybe as an
annotation on init()?)

[JukkaL]

Yeah, that's the reason why this doesn't work right now. Having an __init__ annotation would be a reasonable way to getting to work. Maybe provide a decorator in typing that could be used for this:

from typing import whatever

class A:
    @whatever
    def __init__(self, x: int) -> None: ...

class B(A):
    def __init__(self) -> None: ...  # error!

Not sure what we would call it, though.

[gvanrossum]

This no longer produces an error.