Reported as mock issue 221:http://code.google.com/p/mock/issues/detail?id=221>>> from unittest.mock import Mock>>> m = Mock()>>> m.foo = 3>>> del m.foo>>> m.foo = 4>>> del m.fooTraceback (most recent call last):  File "<stdin>", line 1, in <module>  File "/compile/py3k-cpython/Lib/unittest/mock.py", line 687, in __delattr__    raise AttributeError(name)AttributeError: fooSuggested change:Previous:   def __delattr__(self, name):       if name in _all_magics and name in type(self).__dict__:           delattr(type(self), name)           if name not in self.__dict__:               # for magic methods that are still MagicProxy objects and               # not set on the instance itself               return       if name in self.__dict__:           object.__delattr__(self, name)       obj = self._mock_children.get(name, _missing)       if obj is _deleted:           raise AttributeError(name)       if obj is not _missing:           del self._mock_children[name]       self._mock_children[name] = _deletedChange:   def __delattr__(self, name):       if name in _all_magics and name in type(self).__dict__:           delattr(type(self), name)           if name not in self.__dict__:               # for magic methods that are still MagicProxy objects and               # not set on the instance itself               return       obj = self._mock_children.get(name, _missing)       if name in self.__dict__:           object.__delattr__(self, name)       elif obj is _deleted:           raise AttributeError(name)       if obj is not _missing:           del self._mock_children[name]       self._mock_children[name] = _deletedIncidentally the if ‘obj is not _missing’ line seems superfluous.

I find this to be a reasonable behavior as with normal objects that support setting the attribute after deletion. It also seems to be an easy issue since @michael.foord has already attached the patch for this from the original report. The patch also also causes no test failure on master and a unit test can be added for the behavior once confirmed.

New changeset222d303ade8aadf0adcae5190fac603bdcafe3f0 by Chris Withers (Pablo Galindo) in branch 'master':bpo-20239: Allow repeated deletion of unittest.mock.Mock attributes (#11057)https://github.com/python/cpython/commit/222d303ade8aadf0adcae5190fac603bdcafe3f0

New changesetd358a8cda75446a8e0b5d99149f709395d5eae19 by Chris Withers (Miss Islington (bot)) in branch '3.7':bpo-20239: Allow repeated deletion of unittest.mock.Mock attributes (GH-11629)https://github.com/python/cpython/commit/d358a8cda75446a8e0b5d99149f709395d5eae19