New submission from Karthikeyan Singaravelan <tir.kar...@gmail.com>:
I came across this issue in issue36593 where MagicMock had a custom __class__
attribute set and one of the methods used super() which caused __class__ not to
be set. This seems to have been fixed in the past with issue12370 and a
workaround to alias super at module level and use it was suggested in
msg161704. Usage of the alias seems to solve the issue for Mock but the fix for
__class__ breaks when sys.settrace is set. Example code as below with custom
__class__ defined and with running the code under sys.settrace() super()
doesn't set __class__ but using _safe_super alias works. Another aspect in the
mock related issue is that the call to super() is under a codepath that is not
executed during normal run but executed when sys.settrace during import itself.
import sys
_safe_super = super
def trace(frame, event, arg):
return trace
if len(sys.argv) > 1:
sys.settrace(trace)
class SuperClass(object):
def __init__(self):
super().__init__()
@property
def __class__(self):
return int
class SafeSuperClass(object):
def __init__(self):
_safe_super(SafeSuperClass, self).__init__()
@property
def __class__(self):
return int
print(isinstance(SuperClass(), int))
print(isinstance(SafeSuperClass(), int))
Running above code with trace and without trace
➜ cpython git:(master) ✗ ./python.exe /tmp/buz.py
True
True
➜ cpython git:(master) ✗ ./python.exe /tmp/buz.py 1
False
True
There is a test for the above in Lib/test/test_super.py at
https://github.com/python/cpython/blob/4c409beb4c360a73d054f37807d3daad58d1b567/Lib/test/test_super.py#L87
Add a trace as below in test_super.py at the top and the test case fails
import sys
def trace(frame, event, arg):
return trace
sys.settrace(trace)
➜ cpython git:(master) ✗ ./python.exe Lib/test/test_super.py
....................F
======================================================================
FAIL: test_various___class___pathologies (__main__.TestSuper)
----------------------------------------------------------------------
Traceback (most recent call last):
File "Lib/test/test_super.py", line 100, in test_various___class___pathologies
self.assertEqual(x.__class__, 413)
AssertionError: <class
'__main__.TestSuper.test_various___class___pathologies.<locals>.X'> != 413
----------------------------------------------------------------------
Ran 21 tests in 0.058s
FAILED (failures=1)
----------
components: Interpreter Core
messages: 339988
nosy: benjamin.peterson, eric.snow, michael.foord, ncoghlan, nedbat, xtreak
priority: normal
severity: normal
status: open
title: calling super() causes __class__ to be not defined when
sys.settrace(trace) is set
type: behavior
versions: Python 3.8
_______________________________________
Python tracker <rep...@bugs.python.org>
<https://bugs.python.org/issue36606>
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