mock raises exception when using a spec with an attribute that raises exception on access

@ambv

BPO	45756
Nosy	@ambv, @hongweipeng, @tirkarthi, @sobolevn, @jaap3
PRs	bpo-45756: do not execute `@property` descrs while creating mock autospecs #29901 bpo-45756: Fix mock triggers dynamic lookup via the descriptor protocol. #31348

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

Show more details

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2021-11-08.19:47:53.494>
labels = ['type-bug', '3.8', '3.9', '3.10', '3.11']
title = 'mock raises exception when using a spec with an attribute that raises exception on access'
updated_at = <Date 2022-02-15.06:36:26.841>
user = 'https://bugs.python.org/kjamieson'

bugs.python.org fields:

activity = <Date 2022-02-15.06:36:26.841>
actor = 'hongweipeng'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = []
creation = <Date 2021-11-08.19:47:53.494>
creator = 'kjamieson'
dependencies = []
files = []
hgrepos = []
issue_num = 45756
keywords = ['patch']
message_count = 3.0
messages = ['405982', '406284', '406452']
nosy_count = 6.0
nosy_names = ['lukasz.langa', 'hongweipeng', 'xtreak', 'sobolevn', 'kjamieson', 'jaap3']
pr_nums = ['29901', '31348']
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue45756'
versions = ['Python 3.8', 'Python 3.9', 'Python 3.10', 'Python 3.11']

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 test.py
from unittest import mock

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

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

# python3.11 test.py
Traceback (most recent call last):
  File "/root/test.py", line 8, in <module>
    m = mock.MagicMock(spec=Foo())
        ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.11/unittest/mock.py", line 2069, in __init__
    _safe_super(MagicMixin, self).__init__(*args, **kw)
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.11/unittest/mock.py", line 1087, in __init__
    _safe_super(CallableMixin, self).__init__(
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.11/unittest/mock.py", line 442, in __init__
    self._mock_add_spec(spec, spec_set, _spec_as_instance, _eat_self)
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.11/unittest/mock.py", line 497, in _mock_add_spec
    if iscoroutinefunction(getattr(spec, attr, None)):
                           ^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/root/test.py", line 6, in bar
    raise Exception('xxx')
    ^^^^^^^^^^^^^^^^^^^^^^
Exception: xxx

I think I encountered this when trying to mock requests.Response: psf/requests#5944

This seems to be similar to https://bugs.python.org/issue41768 .

Closing as duplicate of #85934

Navigation Menu

Repository navigation

mock raises exception when using a spec with an attribute that raises exception on access #89917

Metadata

Assignees

Labels

Projects

Milestone

Relationships

Development

mock raises exception when using a spec with an attribute that raises exception on access #89917

Description

Activity

kjamieson commented on Nov 8, 2021

jaap3 commented on Nov 13, 2021

tirkarthi commented on Nov 17, 2021

carljm commented on May 5, 2023

Metadata

Metadata

Assignees

Labels

Projects

Milestone

Relationships

Development

Issue actions