When using a mock and deleting a attribute reset_mock cannot be used anymore since it tries to call reset_mock on the _deleted sentinel value. Reproduction path: ``` from unittest.mock import MagicMock mock = MagicMock() mock.a = 'test' del mock.a mock.reset_mock() ``` Gives: ``` Traceback (most recent call last): File "<stdin>", line 1, in <module> File "/usr/lib/python3.5/unittest/mock.py", line 544, in reset_mock child.reset_mock(visited) AttributeError: '_SentinelObject' object has no attribute 'reset_mock' ``` Expected result: mock is reset without throwing an exception and the 'a' attribute is no longer in a deleted state Only checked 3.5 and current master if bug is present

Can confirm this behavior on CPython master as well. It seems that when an attribute is deleted then a deleted flag is set for the attribute at https://github.com/python/cpython/blob/73820a60cc3c990abb351540ca27bf7689bce8ac/Lib/unittest/mock.py#L737 . But when reset_mock is called it doesn't check for the deleted flag at https://github.com/python/cpython/blob/73820a60cc3c990abb351540ca27bf7689bce8ac/Lib/unittest/mock.py#L543 ➜ cpython git:(master) ./python.exe ../backups/bpo31177.py Traceback (most recent call last): File "../backups/bpo31177.py", line 5, in <module> m.reset_mock() File "/Users/karthikeyansingaravelan/stuff/python/cpython/Lib/unittest/mock.py", line 546, in reset_mock child.reset_mock(visited) AttributeError: '_SentinelObject' object has no attribute 'reset_mock' A simple patch would be to skip the deleted as below but some of the code in mock module raise an AttributeError. I don't know the correct behavior here. But applying the below patch and running tests with `./python.exe Lib/unittest/test/` doesn't cause any test failure. diff --git a/Lib/unittest/mock.py b/Lib/unittest/mock.py index db1e642c00..700e2fb8b9 100644 --- a/Lib/unittest/mock.py +++ b/Lib/unittest/mock.py @@ -541,7 +541,7 @@ class NonCallableMock(Base): self._mock_side_effect = None for child in self._mock_children.values(): - if isinstance(child, _SpecState): + if isinstance(child, _SpecState) or child is _deleted: continue child.reset_mock(visited) I will try to make a PR if it's ok. Thanks

Adding Michael for thoughts on the fix and desired behavior. Removing 3.5 since only security fixes are accepted and adding 3.8 which is also affected. Thanks

I suggest that after reset_mock(), deleted attributes should be available again. In other words, their deletion is reset. I'm opening a PR to this effect. I reported this issue to testing-cabal's mock repo in May 2016 (https://github.com/testing-cabal/mock/pull/361), but my original PR there just avoided an exception without reinstating the deleted attribute.

 New changeset edeca92c84a3b08902ecdfe987cde00c7e617887 by Victor Stinner (Xtreak) in branch 'master': bpo-31177: Skip deleted attributes while calling reset_mock (GH-9302) https://github.com/python/cpython/commit/edeca92c84a3b08902ecdfe987cde00c7e617887 

 New changeset c0566e0ff6c2dd1a8b814ecd65649605c090527b by Miss Islington (bot) in branch '3.6': bpo-31177: Skip deleted attributes while calling reset_mock (GH-9302) https://github.com/python/cpython/commit/c0566e0ff6c2dd1a8b814ecd65649605c090527b 

 New changeset 422c1658b7d34fdc73c5fc895b135862103d1983 by Miss Islington (bot) in branch '3.7': bpo-31177: Skip deleted attributes while calling reset_mock (GH-9302) https://github.com/python/cpython/commit/422c1658b7d34fdc73c5fc895b135862103d1983 

I am closing this as fixed since all the PRs were merged. Feel free to reopen this if needed. Thanks @mariocj89 and @vstinner for the review.