[issue41295] CPython 3.8.4 regression on __setattr__ in multiinheritance with metaclasses

[Stefan Behnel]

Change by Stefan Behnel :


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resolution:  -> fixed
stage: patch review -> resolved
status: open -> closed

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[issue41295] CPython 3.8.4 regression on __setattr__ in multiinheritance with metaclasses

[Łukasz Langa]

Łukasz Langa  added the comment:

Released.

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priority: release blocker -> critical

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[issue41295] CPython 3.8.4 regression on __setattr__ in multiinheritance with metaclasses

[Guido van Rossum]

Guido van Rossum  added the comment:

@Łukasz: this should be good for the 3.8.5 release.

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[issue41295] CPython 3.8.4 regression on __setattr__ in multiinheritance with metaclasses

[kam193]

kam193  added the comment:

@Jonas: I know, running those tests isn't so easy, I think a few libraries are 
incompatible with python 3.9/3.10 yet or I didn't find right prerequisites. But 
fortunately, everything is running on patched 3.8, so after back-porting I can 
run it

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[issue41295] CPython 3.8.4 regression on __setattr__ in multiinheritance with metaclasses

[Stefan Behnel]

Stefan Behnel  added the comment:

> test_asyncio altered the execution environment

That happened several times before in previous builds. I think there's just a 
part of the asyncio tests that is unreliable. I left a comment in issue 41273 
since it might be related, the sporadic failures started appearing in the build 
following the merge.

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[issue41295] CPython 3.8.4 regression on __setattr__ in multiinheritance with metaclasses

[Jonas Schäfer]

Jonas Schäfer  added the comment:

@kam193 Thanks for running the aioxmpp tests. I built the patched python 
yesterday, but I didn’t manage to get a virtualenv with it up

Good to hear that the fix works as expected!

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[issue41295] CPython 3.8.4 regression on __setattr__ in multiinheritance with metaclasses

[kam193]

kam193  added the comment:

@Stefan: Today I run unit tests for Flask-SQLAlchemy (v2.4.3) as well as for 
aioxmpp (another library reported this problem 
https://github.com/horazont/aioxmpp/issues/342). In both cases patch is 
successful: tests fail on Python 3.8.4 but pass on patched Python.

As for me it looks done. Thanks for everyone involved!

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[issue41295] CPython 3.8.4 regression on __setattr__ in multiinheritance with metaclasses

[Guido van Rossum]

Guido van Rossum  added the comment:

We have a buildbot failure: test_asyncio altered the execution environment. 
What does that mean? Victor?

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nosy: +gvanrossum

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[issue41295] CPython 3.8.4 regression on __setattr__ in multiinheritance with metaclasses

[miss-islington]

miss-islington  added the comment:


New changeset 38d930f2ccbff6f93c4c54a7a6a1759266136504 by Miss Islington (bot) 
in branch '3.8':
bpo-41295: Reimplement the Carlo Verre "hackcheck" (GH-21528)
https://github.com/python/cpython/commit/38d930f2ccbff6f93c4c54a7a6a1759266136504


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[issue41295] CPython 3.8.4 regression on __setattr__ in multiinheritance with metaclasses

[miss-islington]

miss-islington  added the comment:


New changeset 01ab9634601fc1a4f9ac5d72ddc022239d2543fe by Miss Islington (bot) 
in branch '3.9':
bpo-41295: Reimplement the Carlo Verre "hackcheck" (GH-21528)
https://github.com/python/cpython/commit/01ab9634601fc1a4f9ac5d72ddc022239d2543fe


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[issue41295] CPython 3.8.4 regression on __setattr__ in multiinheritance with metaclasses

[miss-islington]

miss-islington  added the comment:


New changeset c53b310e5926266ce267c44a168165cacd786d6e by scoder in branch 
'master':
bpo-41295: Reimplement the Carlo Verre "hackcheck" (GH-21528)
https://github.com/python/cpython/commit/c53b310e5926266ce267c44a168165cacd786d6e


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[issue41295] CPython 3.8.4 regression on __setattr__ in multiinheritance with metaclasses

[miss-islington]

Change by miss-islington :


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pull_requests: +20683
pull_request: https://github.com/python/cpython/pull/21541

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[issue41295] CPython 3.8.4 regression on __setattr__ in multiinheritance with metaclasses

[miss-islington]

Change by miss-islington :


--
pull_requests: +20682
pull_request: https://github.com/python/cpython/pull/21540

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[issue41295] CPython 3.8.4 regression on __setattr__ in multiinheritance with metaclasses

[Stefan Behnel]

Stefan Behnel  added the comment:

PR 21528 works for all four test cases that we now have (1x test_capi.py, 3x 
test_descr.py).

Any comments? We need to merge a fix before Monday to meet the deadline of the 
planned hotfix release.

@kam193, could you please also test that change with your real code?

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[issue41295] CPython 3.8.4 regression on __setattr__ in multiinheritance with metaclasses

[Stefan Behnel]

Change by Stefan Behnel :


--
pull_requests: +20664
pull_request: https://github.com/python/cpython/pull/21528

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[issue41295] CPython 3.8.4 regression on __setattr__ in multiinheritance with metaclasses

[David Caro]

David Caro  added the comment:

> David, which issue number is this?

It's issue41295, pr #21473

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[issue41295] CPython 3.8.4 regression on __setattr__ in multiinheritance with metaclasses

[Matthias Klose]

Matthias Klose  added the comment:

David, which issue number is this?

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[issue41295] CPython 3.8.4 regression on __setattr__ in multiinheritance with metaclasses

[Jonas Schäfer]

Change by Jonas Schäfer :


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nosy: +jssfr

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[issue41295] CPython 3.8.4 regression on __setattr__ in multiinheritance with metaclasses

[David Caro]

David Caro  added the comment:

Just sent a PR that fixes the issue (a first approach), let me know if it's 
addressing the issue correctly or if there's a better way.


Thanks!

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[issue41295] CPython 3.8.4 regression on __setattr__ in multiinheritance with metaclasses

[David Caro]

Change by David Caro :


--
keywords: +patch
nosy: +David Caro
nosy_count: 5.0 -> 6.0
pull_requests: +20617
stage:  -> patch review
pull_request: https://github.com/python/cpython/pull/21473

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[issue41295] CPython 3.8.4 regression on __setattr__ in multiinheritance with metaclasses

[David Lord]

David Lord  added the comment:

It appears to be solved in Flask-SQLAlchemy's development version already, as 
the mixins now inherit from `type`. We caught the issue when we started 
applying flake8 (possibly through flake8-bugbear).

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[issue41295] CPython 3.8.4 regression on __setattr__ in multiinheritance with metaclasses

[Christian Heimes]

Christian Heimes  added the comment:

Stefan, please take a look.

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nosy: +scoder

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[issue41295] CPython 3.8.4 regression on __setattr__ in multiinheritance with metaclasses

[Christian Heimes]

Christian Heimes  added the comment:

The regression was introduced in commit 8912c182455de83e27d5c120639ec91b18247913

$ git checkout v3.8.4
$ ./configure -C
$ make
$ $ ./python bpo41295.py 
Traceback (most recent call last):
  File "bpo41295.py", line 14, in 
obj.test = True
  File "bpo41295.py", line 3, in __setattr__
type.__setattr__(cls, key, value)
TypeError: can't apply this __setattr__ to DefaultMeta object

$ git revert 8912c182455de83e27d5c120639ec91b18247913
[detached HEAD 8d3c7847a0] Revert "bpo-39960: Allow heap types in the "Carlo 
Verre" hack check that override "tp_setattro()" (GH-21092) (GH-21339)"
 3 files changed, 11 insertions(+), 117 deletions(-)
$ make
$ ./python bpo41295.py 
True

--
keywords: +3.9regression
priority: normal -> release blocker
versions: +Python 3.10, Python 3.9
Added file: https://bugs.python.org/file49316/bpo41295.py

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[issue41295] CPython 3.8.4 regression on __setattr__ in multiinheritance with metaclasses

[Christian Heimes]

Christian Heimes  added the comment:

The error message is coming from hackcheck function in Objects/typeobject.c, 
https://github.com/python/cpython/blob/b4cd77de05e5bbaa6a4be90f710b787e0790c36f/Objects/typeobject.c#L5811-L5845
 . The issue could be related to bpo-39960. Checking now...

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nosy: +christian.heimes

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[issue41295] CPython 3.8.4 regression on __setattr__ in multiinheritance with metaclasses

[Christian Heimes]

Change by Christian Heimes :


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keywords: +3.8regression
nosy: +lukasz.langa

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[issue41295] CPython 3.8.4 regression on __setattr__ in multiinheritance with metaclasses

[kam193]

New submission from kam193 :

CPython 3.8.4 broke previously correct custom __setattr__ implementation, when 
metaclass inheritances from multiple classes, including not-meta.

Following code:

```
class Meta(type):
def __setattr__(cls, key, value):
type.__setattr__(cls, key, value)

class OtherClass:
pass


class DefaultMeta(OtherClass, Meta):
pass

obj = DefaultMeta('A', (object,), {})
obj.test = True
print(obj.test)
```

Works in Python up to 3.8.3, but in 3.8.4 it raises:

Traceback (most recent call last):
  File "repr.py", line 13, in 
obj.test = True
  File "repr.py", line 3, in __setattr__
type.__setattr__(cls, key, value)
TypeError: can't apply this __setattr__ to DefaultMeta object

This change affects e.g. https://github.com/pallets/flask-sqlalchemy/issues/852

--
messages: 373637
nosy: kam193
priority: normal
severity: normal
status: open
title: CPython 3.8.4 regression on __setattr__ in multiinheritance with 
metaclasses
type: behavior
versions: Python 3.8

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