[issue29822] inspect.isabstract does not work on abstract base classes during __init_subclass__

[Serhiy Storchaka]

Serhiy Storchaka added the comment:

Thank you for your contribution Nate.

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resolution:  -> fixed
stage: backport needed -> resolved
status: open -> closed

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[issue29822] inspect.isabstract does not work on abstract base classes during __init_subclass__

[Serhiy Storchaka]

Serhiy Storchaka added the comment:


New changeset 09b6c0c71ea944f7e8b46998f3ebaf5b9fbe15f6 by Serhiy Storchaka 
(Nate) in branch '3.6':
[3.6] bpo-29822: make inspect.isabstract() work during __init_subclass__ (#1979)
https://github.com/python/cpython/commit/09b6c0c71ea944f7e8b46998f3ebaf5b9fbe15f6


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[issue29822] inspect.isabstract does not work on abstract base classes during __init_subclass__

[Nate Soares]

Changes by Nate Soares :


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[issue29822] inspect.isabstract does not work on abstract base classes during __init_subclass__

[Serhiy Storchaka]

Changes by Serhiy Storchaka :


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stage: patch review -> backport needed
versions:  -Python 3.5

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[issue29822] inspect.isabstract does not work on abstract base classes during __init_subclass__

[Serhiy Storchaka]

Serhiy Storchaka added the comment:


New changeset fcfe80ec2592fed8b3941c79056a8737abef7d3b by Serhiy Storchaka 
(Nate) in branch 'master':
bpo-29822: Make inspect.isabstract() work during __init_subclass__. (#678)
https://github.com/python/cpython/commit/fcfe80ec2592fed8b3941c79056a8737abef7d3b


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[issue29822] inspect.isabstract does not work on abstract base classes during __init_subclass__

[Serhiy Storchaka]

Serhiy Storchaka added the comment:

LGTM, but would be nice if Yury and Nick take a look.

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[issue29822] inspect.isabstract does not work on abstract base classes during __init_subclass__

[Serhiy Storchaka]

Changes by Serhiy Storchaka :


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nosy: +ncoghlan

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[issue29822] inspect.isabstract does not work on abstract base classes during __init_subclass__

[Nate Soares]

Nate Soares added the comment:

I didn't know about issue29638, and I'm not sure whether my PR fixes it. 
Looking at that bug, I don't think that my PR would fix it, because I still 
trust TPFLAGS_IS_ABSTRACT when __abstractmethods__ exists. That said, I'm not 
clear on how the cache works, so it's possible that my PR would fix 29638.

My issue appears when one uses py3.6's new __init_subclass__ hook with an ABC. 
__init_subclass__ is run by type.__new__, which means that, as of py3.6, users 
can (in a natural/reasonable way) inspect ABCMeta classes before 
ABCMeta.__new__ finishes executing. I didn't see any reasonable way to have 
ABCMeta.__new__ finish setting up the ABC before calling super().__new__, so I 
figured the fix should go into inspect.isabstract. But there may be better 
solutions I just didn't think of.

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[issue29822] inspect.isabstract does not work on abstract base classes during __init_subclass__

[Serhiy Storchaka]

Serhiy Storchaka added the comment:

Is this an alternate fix of issue29638?

--
components: +Library (Lib)
nosy: +yselivanov
stage:  -> patch review
type:  -> behavior
versions: +Python 3.5, Python 3.6

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[issue29822] inspect.isabstract does not work on abstract base classes during __init_subclass__

[Ivan Levkivskyi]

Ivan Levkivskyi added the comment:

Serhiy, sorry for a distraction, but it looks like here is one more situation 
where inspect.isabstract is problematic, similar to what was discussed in 
http://bugs.python.org/issue29638 recently.

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nosy: +levkivskyi, serhiy.storchaka

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[issue29822] inspect.isabstract does not work on abstract base classes during __init_subclass__

[Nate Soares]

Changes by Nate Soares :


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pull_requests: +556

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[issue29822] inspect.isabstract does not work on abstract base classes during __init_subclass__

[Nate Soares]

New submission from Nate Soares:

Here's an example test that fails:

def test_isabstract_during_init_subclass(self):
from abc import ABCMeta, abstractmethod

isabstract_checks = []

class AbstractChecker(metaclass=ABCMeta):
def __init_subclass__(cls):
abstract_checks.append(inspect.isabstract(cls))

class AbstractClassExample(AbstractChecker):

@abstractmethod
def foo(self):
pass

class ClassExample(AbstractClassExample):
def foo(self):
pass

self.assertEqual(isabstract_checks, [True, False])

To run the test, you'll need to be on a version of python where bpo-29581 is 
fixed (e.g., a cpython branch with https://github.com/python/cpython/pull/527 
merged) in order for __init_subclass__ to work with ABCMeta at all in the first 
place. I have a simple patch to inspect.isabstract that fixes this, and will 
make a PR shortly.

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messages: 289682
nosy: So8res
priority: normal
severity: normal
status: open
title: inspect.isabstract does not work on abstract base classes during 
__init_subclass__
versions: Python 3.7

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