[Bug 1841072] Re: test_reflection.CallbackEqualityTest.test_different_instance_callbacks fails on Python 3.8

[Ghanshyam Mann]

This was considered as bugfix in python 3.8 because bound methods should
only be equal if they are bound on the same instance, not if their
instances are equal. In Python <= 3.7 the bound method equality calls
the equivalent of instance1 == instance2 and return true based on that
and while in Python 3.8 it checks if instance1 is instance2.

You can see details about this behavior change in py3.8 
- https://bugs.python.org/issue1617161
- python-dev discussion: https://mail.python.org/pipermail/python-dev/2018-June/153959.html

With that and for cases of 'strict=False', oslo utils is_same_callback() method behaviour also changed. With 'strict=False', this method returned *True* for python <3.7 (because  == comparison used to call the __eq__ method return value) and *False* for python3.8 onwards (because == never call __eq__ method and check the id of self).
-https://github.com/openstack/oslo.utils/blob/7c4a94c0c3fcbd8f05541944851728f30deadd9b/oslo_utils/reflection.py#L172-L174

For 'strict' is True (which is the default) there is no behavior change because is_same_callback() method checks if 'self' of both bound methods are equal or not
- https://github.com/openstack/oslo.utils/blob/7c4a94c0c3fcbd8f05541944851728f30deadd9b/oslo_utils/reflection.py#L183

We should modify the test to test the behaviors this way and in
is_same_callback() method we should clearly document that 'strict' is no
more an option or valid thing for python3.8 onwards and we should even
deprecate this arg itself.

** Bug watch added: Python Roundup #1617161
   http://bugs.python.org/issue1617161

** Changed in: oslo.utils
       Status: New => Confirmed

** Changed in: oslo.utils
     Assignee: (unassigned) => Ghanshyam Mann (ghanshyammann)

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https://bugs.launchpad.net/bugs/1841072

Title:
  test_reflection.CallbackEqualityTest.test_different_instance_callbacks
  fails on Python 3.8

Status in oslo.utils:
  Confirmed
Status in python-oslo.utils package in Ubuntu:
  Fix Released
Status in python3-defaults package in Ubuntu:
  Invalid

Bug description:
  When running the unit test on Python 3.8, it fails with the following
  traceback:

  oslo_utils.tests.test_reflection.CallbackEqualityTest.test_different_instance_callbacks
  ---------------------------------------------------------------------------------------

  Captured traceback:
  ~~~~~~~~~~~~~~~~~~~
      b'Traceback (most recent call last):'
      b'  File "/tmp/oslo.utils/oslo_utils/tests/test_reflection.py", line 156, in test_different_instance_callbacks'
      b'    self.assertTrue(reflection.is_same_callback(b.b, c.b, strict=False))'
      b'  File "/tmp/oslo.utils/.tox/py38/lib/python3.8/site-packages/unittest2/case.py", line 702, in assertTrue'
      b'    raise self.failureException(msg)'
      b'AssertionError: False is not true'
      b''

  This is apparently caused by a behavior change in Python 3.8 due to
  [1]. I have confirmed the different behavior by running tests manually
  on 3.6, 3.7 (both return True) and 3.8.

  According to [2], only taskflow seems to be using that method now, and
  it is not changing the default value for the "strict" parameter.

  [1] - https://bugs.python.org/issue1617161
  [2] - http://codesearch.openstack.org/?q=is_same_callback&i=nope&files=&repos=

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