[issue39578] MagicMock specialisation instance can no longer be passed to new MagicMock instance

[Elena Oat]

Elena Oat  added the comment:

Here's the example I ran, that indeed fails in Python 3.8 and Python 3.9 (with 
different errors) and works in Python 3.7. 

from unittest.mock import MagicMock


class CustomMock(MagicMock):
def __init__(self):
super().__init__(__something__='something')


mock = CustomMock()
MagicMock(mock)


In Python 3.8 the error is TypeError: __init__() got an unexpected keyword 
argument '_new_parent'. 

In Python 3.9 the error is TypeError: __init__() got an unexpected keyword 
argument 'name'.

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[issue39578] MagicMock specialisation instance can no longer be passed to new MagicMock instance

[Elena Oat]

Elena Oat  added the comment:

I am looking at reproducing this and creating a short example of where this 
fails. Will look further into more details of why this doesn't work.

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[issue39578] MagicMock specialisation instance can no longer be passed to new MagicMock instance

[Mario Corchero]

Mario Corchero  added the comment:

Having not looked deeply at it but with the reproducer, running a quick bisect, 
it points to this commit: 
https://github.com/python/cpython/commit/77b3b7701a34ecf6316469e05b79bb91de2addfa
 
I'll try having a look later at the day if I can manage to free some time.

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[issue39578] MagicMock specialisation instance can no longer be passed to new MagicMock instance

[Frank Harrison]

Frank Harrison  added the comment:

Minor correction: The regression was only tested on Python 3.9.0a2 (Fedora), 
Python 3.9a3 (OSX), CPython's master (build from source) and the latest 
non-prerelease versions of python 3.5, 3.6, 3.7, and 3.8. Tested on OSX and 
Fedora 31.

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[issue39578] MagicMock specialisation instance can no longer be passed to new MagicMock instance

[Karthikeyan Singaravelan]

Change by Karthikeyan Singaravelan :


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nosy: +cjw296, lisroach, mariocj89, michael.foord, xtreak

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[issue39578] MagicMock specialisation instance can no longer be passed to new MagicMock instance

[Frank Harrison]

New submission from Frank Harrison :

This is my first bug logged here, I've tried to follow the guideline and search 
for this issue; please let me know if I missed anything.

Summary:
unittest.mock.MagicMock has a regression starting in 3.8. The regression was 
only tested on latest non-prerelease versions of python 3.5, 3.6, 3.7, 3.8 and 
3.9. Tested on OSX and Fedora 31.

Repro:
--
If you create an instance of a MagicMock specialisation with parameters to 
__init__(),  you can no longer pass that instance to the __init__() function of 
another MagicMock object e.g. a base-class is replaced with MagicMock. See the 
unittests bellow for more details, use-cases and fail situations.

What happens:
-
Here's a python3.9 example traceback. It may be worth noting that there is a 
difference in the tracebacks between 3.8 and 3.9.

Traceback (most recent call last):
  File "<...>", line <..>, in test_raw_magic_moc_passing_thru_single_pos
mock_object = mock.MagicMock(mock_param)  # error is here, instantiating 
another object
  File "/usr/lib64/python3.9/unittest/mock.py", line 408, in __new__
if spec_arg and _is_async_obj(spec_arg):
  File "/usr/lib64/python3.9/unittest/mock.py", line 2119, in __get__
return self.create_mock()
  File "/usr/lib64/python3.9/unittest/mock.py", line 2112, in create_mock
m = parent._get_child_mock(name=entry, _new_name=entry,
  File "/usr/lib64/python3.9/unittest/mock.py", line 1014, in _get_child_mock
return klass(**kw)
TypeError: __init__() got an unexpected keyword argument 'name'


Code demonstrating the problem:
---

import unittest

from unittest import mock


class TestMockMagicAssociativeHierarchies(unittest.TestCase):
""" Mimicing real-world testing where we mock a base-class

The intent here is to demonstrate some of the requirements of associative-
hierarchies e.g. where a class may have its associative-parent set at
run-time, rather that defining it via a class-hierarchy. Obviously this
also needs to work with class-hierarchies, that is an associative-parent is
likely to be a specialisation of some interface, usually one that is being
mocked.

For example tkinter and Qt have both a class-hierarchy and a layout-
hierarchy; the latter is modifyable at runtime.

Most of the tests here mimic a specialisation of an upstream object (say a
tk.Frame class), instantiating that specialisation and then passing it to
another object. The reason behind this is an observed regression in Python
3.8.
"""
def test_raw_magic_moc_passing_thru_no_params(self):
""" REGRESSION: Python3.8 (inc Python3.9)

Create a mocked specialisation passing it to another mock.

One real-world use-case for this is simple cases where we simply want to
define a new convenience type that forces a default configuration of
the inherited type (calls super().__init__()).
"""
class MockSubCallsParentInit(mock.MagicMock):
def __init__(self):
super().__init__()  # intentionally empty
mock_param = MockSubCallsParentInit()
mock_object = mock.MagicMock(mock_param)  # error is here, 
instantiating another object
self.assertIsInstance(mock_object, mock.MagicMock)

def test_raw_magic_moc_passing_thru_single_pos(self):
""" REGRESSION: Python3.8 (inc Python3.9)

Same as test_raw_magic_moc_no_init_params() but we want to specialise
with positional arguments. """
class MockSubCallsParentInitWithPositionalParam(mock.MagicMock):
def __init__(self):
super().__init__("specialise init calls")
mock_param = MockSubCallsParentInitWithPositionalParam()
mock_object = mock.MagicMock(mock_param)  # error is here, 
instantiating another object
self.assertIsInstance(mock_object, mock.MagicMock)

def test_raw_magic_moc_passing_thru_single_kwarg(self):
""" REGRESSION: Python3.8 (inc Python3.9)

Same as test_raw_magic_moc_passing_thru_single_pos() but we want to
specialise with a key-word argument. """
class MockSubCallsParentInitWithPositionalParam(mock.MagicMock):
def __init__(self):
super().__init__(__some_key_word__="some data")
mock_param = MockSubCallsParentInitWithPositionalParam()
mock_object = mock.MagicMock(mock_param)  # error is here, 
instantiating another object
self.assertIsInstance(mock_object, mock.MagicMock)

def test_mock_as_param_no_inheritance(self):
""" PASSES 

Mimic mocking out types, without type specialisation.
for example in pseudo code 
tk.Frame = mock.MagicMock; tk.Frame(t.Frame) """
mock_param = mock.MagicMock()
mock_object = mock.MagicMock(mock_param)
self.assertIsInstance(mock_object, mock.MagicMock)

def