Python 3.9.2 (default, Mar 1 2021, 08:18:55) [MSC v.1916 64 bit (AMD64)] on win32
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>>> class Foo:
... def a(): pass
...
>>> Foo.a = None
>>> Foo().a()
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: 'NoneType' object is not callable
>>>