[issue36593] Trace function interferes with MagicMock isinstance?

[Karthikeyan Singaravelan]

Karthikeyan Singaravelan <tir.karthi at gmail.com> added the comment:

There are very few changes to mock.py on bisecting with the example in the report is d358a8cda75446a8e0b5d99149f709395d5eae19 the problem? I am surprised by the reason this commit leads to change in behavior with set trace.

➜  cpython git:(master) ✗ cat ../backups/bpo36593.py
import sys

def trace(frame, event, arg):
    return trace

if len(sys.argv) > 1:
    sys.settrace(trace)

from unittest.mock import MagicMock

class A:
    pass

m = MagicMock(spec=A)
print("isinstance: ", isinstance(m, A))
➜  cpython git:(master) ✗ git checkout d358a8cda75446a8e0b5d99149f709395d5eae19 Lib/unittest/mock.py
➜  cpython git:(master) ✗ ./python.exe ../backups/bpo36593.py 1
isinstance:  False
➜  cpython git:(master) ✗ git checkout d358a8cda75446a8e0b5d99149f709395d5eae19~1 Lib/unittest/mock.py
➜  cpython git:(master) ✗ ./python.exe ../backups/bpo36593.py 1
isinstance:  True

commit d358a8cda75446a8e0b5d99149f709395d5eae19
Author: Miss Islington (bot) <31488909+miss-islington at users.noreply.github.com>
Date:   Mon Jan 21 01:37:54 2019 -0800

    bpo-20239: Allow repeated deletion of unittest.mock.Mock attributes (GH-11629)

    * Allow repeated deletion of unittest.mock.Mock attributes

    * fixup! Allow repeated deletion of unittest.mock.Mock attributes

    * fixup! fixup! Allow repeated deletion of unittest.mock.Mock attributes
    (cherry picked from commit 222d303ade8aadf0adcae5190fac603bdcafe3f0)

    Co-authored-by: Pablo Galindo <Pablogsal at gmail.com>

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nosy: +pablogsal

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue36593>
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