def just_warn(*args, **kw):
        """
        We only warn on Python 3 because we are not aware of any concrete
        consequences of not setting the cell on Python 2.
        """
        warnings.warn(
            "Running interpreter doesn't sufficiently support code object "
            "introspection.  Some features like bare super() or accessing "
            "__class__ will not work with slotted classes.",
            RuntimeWarning,
            stacklevel=2,
        )

        We only warn on Python 3 because we are not aware of any concrete
        consequences of not setting the cell on Python 2.
        
stackoverflow/venv/lib/python3.6/site-packages/attr/_compat.py