class SlotsCM:
    __slots__ = ("__enter__", "__exit__", )
    def __init__(self):
        self.__enter__ = self.__exit__ = lambda *__: None
# This works
with SlotsCM():
    pass
# This doesn't.
from contextllib import ExitStack
with ExitStack() as stack:
    stack.enter_context(SlotsCM())

Traceback (most recent call last):
  File "xxxx.py", line 16, in <module>
    stack.enter_context(SlotsCM())
    ~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^
  File "......../contextlib.py", line 530, in enter_context
    result = _enter(cm)
TypeError: 'member_descriptor' object is not callable