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Title: mock raises exception when using a spec with an attribute that raises exception on access
Type: behavior Stage: patch review
Components: Versions: Python 3.11, Python 3.10, Python 3.9, Python 3.8
Status: open Resolution:
Dependencies: Superseder:
Assigned To: Nosy List: hongweipeng, jaap3, kjamieson, lukasz.langa, sobolevn, xtreak
Priority: normal Keywords: patch

Created on 2021-11-08 19:47 by kjamieson, last changed 2022-04-11 14:59 by admin.

Pull Requests
URL Status Linked Edit
PR 29901 open sobolevn, 2021-12-03 08:22
PR 31348 open hongweipeng, 2022-02-15 06:36
Messages (3)
msg405982 - (view) Author: Kevin Jamieson (kjamieson) Date: 2021-11-08 19:47
In Python 3.8 and later creating a mock with a spec specifying an object containing a property that happens to raise an exception when accessed will fail, because _mock_add_spec calls getattr() on every attribute of the spec. This did not happen in Python 3.6/3.7.

This is likely a fairly unusual scenario (and in the particular case where I encountered this I could just use a class instead of an instance for the spec), but it was surprising.

For example:

# cat
from unittest import mock

class Foo:
    def bar(self) -> str:
        raise Exception('xxx')

m = mock.MagicMock(spec=Foo())

# python3.11
Traceback (most recent call last):
  File "/root/", line 8, in <module>
    m = mock.MagicMock(spec=Foo())
  File "/usr/lib/python3.11/unittest/", line 2069, in __init__
    _safe_super(MagicMixin, self).__init__(*args, **kw)
  File "/usr/lib/python3.11/unittest/", line 1087, in __init__
    _safe_super(CallableMixin, self).__init__(
  File "/usr/lib/python3.11/unittest/", line 442, in __init__
    self._mock_add_spec(spec, spec_set, _spec_as_instance, _eat_self)
  File "/usr/lib/python3.11/unittest/", line 497, in _mock_add_spec
    if iscoroutinefunction(getattr(spec, attr, None)):
  File "/root/", line 6, in bar
    raise Exception('xxx')
Exception: xxx
msg406284 - (view) Author: Jaap Roes (jaap3) Date: 2021-11-13 16:00
I think I encountered this when trying to mock `requests.Response`:
msg406452 - (view) Author: Karthikeyan Singaravelan (xtreak) * (Python committer) Date: 2021-11-17 04:38
This seems to be similar to .
Date User Action Args
2022-04-11 14:59:52adminsetgithub: 89917
2022-02-15 06:36:26hongweipengsetnosy: + hongweipeng
pull_requests: + pull_request29497
2021-12-03 08:46:16AlexWaygoodsetnosy: + lukasz.langa
2021-12-03 08:22:21sobolevnsetkeywords: + patch
nosy: + sobolevn

pull_requests: + pull_request28125
stage: patch review
2021-11-17 04:38:10xtreaksetnosy: + xtreak
messages: + msg406452
2021-11-13 16:00:51jaap3setnosy: + jaap3
messages: + msg406284
2021-11-08 19:47:53kjamiesoncreate