[issue32999] issubclass(obj, abc.ABC) causes a segfault

[miss-islington]

miss-islington  added the comment:


New changeset c71edab15d023360388da8360700d419b5f48c81 by Miss Islington (bot) 
in branch '3.7':
bpo-32999: ast: Convert useless check to assert (GH-6197)
https://github.com/python/cpython/commit/c71edab15d023360388da8360700d419b5f48c81


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[issue32999] issubclass(obj, abc.ABC) causes a segfault

[miss-islington]

Change by miss-islington :


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[issue32999] issubclass(obj, abc.ABC) causes a segfault

[INADA Naoki]

INADA Naoki  added the comment:


New changeset c65bf3fe4a2bde424b79e350f36b7aaa3f6476f6 by INADA Naoki in branch 
'master':
bpo-32999: ast: Convert useless check to assert (GH-6197)
https://github.com/python/cpython/commit/c65bf3fe4a2bde424b79e350f36b7aaa3f6476f6


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[issue32999] issubclass(obj, abc.ABC) causes a segfault

[INADA Naoki]

Change by INADA Naoki :


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[issue32999] issubclass(obj, abc.ABC) causes a segfault

[Ivan Levkivskyi]

Ivan Levkivskyi  added the comment:


New changeset 5d8bb5d07be2a9205e7059090f0ac5360d36b217 by Ivan Levkivskyi (Miss 
Islington (bot)) in branch '3.7':
bpo-32999: Revert GH-6002 (fc7df0e6) (GH-6189) (GH-6190)
https://github.com/python/cpython/commit/5d8bb5d07be2a9205e7059090f0ac5360d36b217


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[issue32999] issubclass(obj, abc.ABC) causes a segfault

[miss-islington]

Change by miss-islington :


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[issue32999] issubclass(obj, abc.ABC) causes a segfault

[INADA Naoki]

INADA Naoki  added the comment:


New changeset f757b72b2524ce3451d2269f0b8a9f0593a7b27f by INADA Naoki in branch 
'master':
bpo-32999: Revert GH-6002 (fc7df0e6) (GH-6189)
https://github.com/python/cpython/commit/f757b72b2524ce3451d2269f0b8a9f0593a7b27f


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[issue32999] issubclass(obj, abc.ABC) causes a segfault

[INADA Naoki]

Change by INADA Naoki :


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[issue32999] issubclass(obj, abc.ABC) causes a segfault

[Ivan Levkivskyi]

Ivan Levkivskyi  added the comment:

Serhiy, for example `issubclass(typing.MutableMapping, typing.Mapping)` returns 
`True` while neither of those two are actual class objects. These relationships 
are kept mostly so that `typing.*` can be used as a drop-in replacement for 
`collections.abc.*` (plus backwards compatibility).

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[issue32999] issubclass(obj, abc.ABC) causes a segfault

[Alexey Izbyshev]

Alexey Izbyshev  added the comment:

Sorry for status update, this was due to a concurrent modification.

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status: open -> closed

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[issue32999] issubclass(obj, abc.ABC) causes a segfault

[Alexey Izbyshev]

Alexey Izbyshev  added the comment:

@inada.naoki: I don't question your change. My point is the same as in #33018 
(I've discovered that PR only after I commented). The error message is 
misleading, and it's just a coincidence that a TypeError and not some other 
error is raised when abc attempts to add a non-type object to a WeakSet.

@serhiy.storchaka: Note that an example that you requested is unlikely to be 
related to ABC and probably is more like my artificial __subclasscheck__ 
example. So, making changes just for ABC as suggested in #33018 might make 
sense.

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status: closed -> open

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[issue32999] issubclass(obj, abc.ABC) causes a segfault

[Joshua Bronson]

Change by Joshua Bronson :


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[issue32999] issubclass(obj, abc.ABC) causes a segfault

[INADA Naoki]

Change by INADA Naoki :


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

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[issue32999] issubclass(obj, abc.ABC) causes a segfault

[miss-islington]

miss-islington  added the comment:


New changeset d824b4e4afbe9cf02310e39b14402fb2aa271f8f by Miss Islington (bot) 
in branch '3.7':
bpo-32999: Fix ABC.__subclasscheck__ crash (GH-6002)
https://github.com/python/cpython/commit/d824b4e4afbe9cf02310e39b14402fb2aa271f8f


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[issue32999] issubclass(obj, abc.ABC) causes a segfault

[Joshua Bronson]

Change by Joshua Bronson :


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[issue32999] issubclass(obj, abc.ABC) causes a segfault

[miss-islington]

Change by miss-islington :


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[issue32999] issubclass(obj, abc.ABC) causes a segfault

[INADA Naoki]

INADA Naoki  added the comment:


New changeset fc7df0e664198cb05cafd972f190a18ca422989c by INADA Naoki in branch 
'master':
bpo-32999: Fix ABC.__subclasscheck__ crash (GH-6002)
https://github.com/python/cpython/commit/fc7df0e664198cb05cafd972f190a18ca422989c


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[issue32999] issubclass(obj, abc.ABC) causes a segfault

[INADA Naoki]

INADA Naoki  added the comment:

> BTW, do TypeErrors related to weak references deserve any treatment? Isn't it 
> a kind of coincidence that the error raised due to usage of WeakSet in 
> issubclass(obj, ABC) is what we expect? (Sorry, I'm not familiar with 
> WeakSets).

Sorry, I can't get what is your point.
I don't want to change ABC behavior for now.  I want to make C implementation 
consistent with Python implementation, except some (unrealistic) corner cases.

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[issue32999] issubclass(obj, abc.ABC) causes a segfault

[Serhiy Storchaka]

Serhiy Storchaka  added the comment:

Could you please show examples with __suclasscheck__ returning True for 
non-class objects?

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[issue32999] issubclass(obj, abc.ABC) causes a segfault

[Alexey Izbyshev]

Alexey Izbyshev  added the comment:

OK, making a new implementation behave as the old one is fine with me too.

BTW, do TypeErrors related to weak references deserve any treatment? Isn't it a 
kind of coincidence that the error raised due to usage of WeakSet in 
issubclass(obj, ABC) is what we expect? (Sorry, I'm not familiar with WeakSets).

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[issue32999] issubclass(obj, abc.ABC) causes a segfault

[Ivan Levkivskyi]

Ivan Levkivskyi  added the comment:

Actually, the behaviour when __suclasscheck__ returns True for non-class 
objects may be used by some code. Even typing module did this, I tried to 
remove as much as possible of this, but I think there may be few such 
situations left.

Therefore, the patch by Inada-san (that makes C behaviour follow Python 
behaviour) looks reasonable to me.

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[issue32999] issubclass(obj, abc.ABC) causes a segfault

[INADA Naoki]

Change by INADA Naoki :


--
keywords: +patch
pull_requests: +5767
stage:  -> patch review

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[issue32999] issubclass(obj, abc.ABC) causes a segfault

[Alexey Izbyshev]

Change by Alexey Izbyshev :


--
versions: +Python 3.7

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[issue32999] issubclass(obj, abc.ABC) causes a segfault

[Alexey Izbyshev]

Alexey Izbyshev  added the comment:

I've also checked that ABC.register() doesn't allow non-classes (and PEP 3119 
mentions that).

Looking at PyObject_IsSubclass in Objects/abstract.c, the only case in which 
its check_class() could be avoided is if there is a custom __subclasscheck__:

>>> class M(type):
...   def __subclasscheck__(cls, c):
... return c == 1 or super().__subclasscheck__(c)
...
>>> class A(metaclass=M):
...   pass
...
>>> issubclass(1, A)
True

If there is no need to support such weird __subclasscheck__, check_class() 
could be called earlier.

Note, however, that check_class() treats anything having __bases__ as a class, 
so moving the check alone is not enough to avoid the crash in all cases.

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[issue32999] issubclass(obj, abc.ABC) causes a segfault

[Alexey Izbyshev]

Alexey Izbyshev  added the comment:

> Is there any sense in accepting non-types as the first argument of 
> issubclass()?

No, though it is not (clearly) documented. The docs mention TypeError, but only 
for the second argument if my reading is correct.

In practice, issubclass() raises a TypeError if the first argument is not a 
class object:

>>> issubclass(1, int)
Traceback (most recent call last):
  File "", line 1, in 
TypeError: issubclass() arg 1 must be a class

Though, as I mentioned above, behavior for ABCs was always weird.

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[issue32999] issubclass(obj, abc.ABC) causes a segfault

[Serhiy Storchaka]

Serhiy Storchaka  added the comment:

Is there any sense in accepting non-types as the first argument of 
issubclass()? I would add a check just in issubclass().

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versions: +Python 3.7

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[issue32999] issubclass(obj, abc.ABC) causes a segfault

[Alexey Izbyshev]

Alexey Izbyshev  added the comment:

In debug mode, the following assertion fails:

python: ./Modules/_abc.c:642: _abc__abc_subclasscheck_impl: Assertion 
`((PyObject*)(mro))->ob_type))->tp_flags & ((1UL << 26))) != 0)' failed.

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[issue32999] issubclass(obj, abc.ABC) causes a segfault

[Alexey Izbyshev]

New submission from Alexey Izbyshev :

Demo:

>>> from abc import ABC
>>> issubclass(1, ABC)
Segmentation fault (core dumped)

The stack trace is attached.

Before reimplementation of abc in C, the result was confusing too:

Python 3.6.4 (v3.6.4:d48eceb, Dec 19 2017, 06:54:40) [MSC v.1900 64 bit (AMD64)]
 on win32
>>> from abc import ABC
>>> issubclass(1, ABC)
Traceback (most recent call last):
  File "", line 1, in 
  File "abc.py", line 230, in __subclasscheck__
  File "_weakrefset.py", line 84, in add
TypeError: cannot create weak reference to 'int' object

--
components: Extension Modules
files: stack-trace.txt
messages: 313259
nosy: izbyshev, levkivskyi
priority: normal
severity: normal
status: open
title: issubclass(obj, abc.ABC) causes a segfault
type: crash
versions: Python 3.8
Added file: https://bugs.python.org/file47470/stack-trace.txt

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