unittest.mock.Mock.__class__

__class__

Normally the __class__ attribute of an object will return its type. For a mock object with a spec, __class__ returns the spec class instead. This allows mock objects to pass isinstance() tests for the object they are replacing / masquerading as:

>>> mock = Mock(spec=3)
>>> isinstance(mock, int)
True

__class__ is assignable to, this allows a mock to pass an isinstance() check without forcing you to use a spec:

>>> mock = Mock()
>>> mock.__class__ = dict
>>> isinstance(mock, dict)
True