Setter and getter method names can't differ (Python 2)

[JukkaL]

This doesn't work (reported by Tim Abbott):

class C:
    def __init__(self) -> None:
        self._x = 0

    @property
    def x(self) -> int:
        return self._x

    @x.setter
    def set_x(self, value: int) -> None:   # Note the name of the method! "def x" works.
        self._x = value

This example seems to be only valid in Python 2, not Python 3.

(Originally reported in #220 (comment).)

[JukkaL]

Closing due to Python 2 feature freeze (#12237).