[issue42747] Remove Py_TPFLAGS_HAVE_VERSION_TAG flag?

[Petr Viktorin]

Petr Viktorin  added the comment:

I usually wait until buildbots are green before closing the bpo, but I don't 
think there's anything else.

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status: open -> closed

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[issue42747] Remove Py_TPFLAGS_HAVE_VERSION_TAG flag?

[Pablo Galindo Salgado]

Pablo Galindo Salgado  added the comment:

Is there anything left in this issue?

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[issue42747] Remove Py_TPFLAGS_HAVE_VERSION_TAG flag?

[Petr Viktorin]

Petr Viktorin  added the comment:


New changeset 632e8a69593efb12ec58d90e624ddf249a7a1b65 by Miss Islington (bot) 
in branch '3.10':
bpo-42747: Remove Py_TPFLAGS_HAVE_AM_SEND and make Py_TPFLAGS_HAVE_VERSION_TAG 
no-op (GH-27260) (GH-27306)
https://github.com/python/cpython/commit/632e8a69593efb12ec58d90e624ddf249a7a1b65


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[issue42747] Remove Py_TPFLAGS_HAVE_VERSION_TAG flag?

[miss-islington]

miss-islington  added the comment:


New changeset a4760cc32d9e5dac7be262e9736eb30502cd7be3 by Petr Viktorin in 
branch 'main':
bpo-42747: Remove Py_TPFLAGS_HAVE_AM_SEND and make Py_TPFLAGS_HAVE_VERSION_TAG 
no-op (GH-27260)
https://github.com/python/cpython/commit/a4760cc32d9e5dac7be262e9736eb30502cd7be3


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[issue42747] Remove Py_TPFLAGS_HAVE_VERSION_TAG flag?

[miss-islington]

Change by miss-islington :


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pull_request: https://github.com/python/cpython/pull/27306

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[issue42747] Remove Py_TPFLAGS_HAVE_VERSION_TAG flag?

[Petr Viktorin]

Change by Petr Viktorin :


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[issue42747] Remove Py_TPFLAGS_HAVE_VERSION_TAG flag?

[Petr Viktorin]

Petr Viktorin  added the comment:

The bit cannot be repurposed, since older extensions using the stable ABI might 
set it.
It doesn't make much sense to remove the Py_TPFLAGS_HAVE_VERSION_TAG or 
Py_TPFLAGS_HAVE_FINALIZE defines; I'd let them stay to document that the bits 
are reserved.

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[issue42747] Remove Py_TPFLAGS_HAVE_VERSION_TAG flag?

[Petr Viktorin]

Petr Viktorin  added the comment:

> I'm only aware of PyQt which uses the stable ABI. Is there other projects 
> using it? Do these projects check for Py_TPFLAGS_HAVE_VERSION_TAG or 
> Py_TPFLAGS_HAVE_FINALIZE flag?

I think there are. Who knows how many; they're not required to register 
anywhere.


If the flags do end up being removed, it would be nice to reserve the bits (in 
a comment), so they aren't reused too soon.

Also, ISTM that PEP 387 applies, and requires warning for two releases. How can 
that be done for flags?

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[issue42747] Remove Py_TPFLAGS_HAVE_VERSION_TAG flag?

[STINNER Victor]

STINNER Victor  added the comment:

Ah, I see that there is a misunderstanding. The flag is used for two things:

(*) Create/Declare a type

IMO Py_TPFLAGS_HAVE_VERSION_TAG and Py_TPFLAGS_HAVE_FINALIZE are useless for 
that.

(*) Check if a type has the flag

An extension built with the stable ABI *can* use PyType_HasFeature(type, 
Py_TPFLAGS_HAVE_VERSION_TAG).

I'm only aware of PyQt which uses the stable ABI. Is there other projects using 
it? Do these projects check for Py_TPFLAGS_HAVE_VERSION_TAG or 
Py_TPFLAGS_HAVE_FINALIZE flag?

If we cannot be used that no extension module built with the stable ABI for 
these flags, the safe option is to keep them, deprecate them, and always define 
them. For example, add the flags to Py_TPFLAGS_DEFAULT and/or add them in 
type_new() or PyType_Ready().

--

Py_TPFLAGS_HAVE_VERSION_TAG is really an internal tag. It should only be used 
by _PyType_Lookup().

I'm not sure why someone would like to check explicitly for the 
Py_TPFLAGS_HAVE_FINALIZE flag. I would expect that only Python internals call 
the tp_finalize slot.

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[issue42747] Remove Py_TPFLAGS_HAVE_VERSION_TAG flag?

[STINNER Victor]

STINNER Victor  added the comment:

Serhiy Storchaka:
> I don't think that it was right thing to break binary compatibility. It 
> virtually buried the stable ABI.

IMO there is a misunderstanding about the stable ABI. PyType_FromSpec() doesn't 
need Py_TPFLAGS_HAVE_xxx flags: this function allocates a heap type which *has* 
all these members (set to 0/NULL by default).

And it's not possible to define a static type using the limited C API, since 
the PyTypeObject structure is excluded from it on purpose.

See bpo-32388 for a similar discussion.

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[issue42747] Remove Py_TPFLAGS_HAVE_VERSION_TAG flag?

[Serhiy Storchaka]

Serhiy Storchaka  added the comment:

I don't think that it was right thing to break binary compatibility. It 
virtually buried the stable ABI.

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[issue42747] Remove Py_TPFLAGS_HAVE_VERSION_TAG flag?

[Petr Viktorin]

Petr Viktorin  added the comment:

IMO, these flags are useless. Both the stable ABI and the version-specific 
builds of extension modules use the memory layout of the current interpreter 
and fill unset slots with NULL.

Py_TPFLAGS_HAVE_AM_SEND is new in 3.10, so it can  be removed (or replaced by a 
check for Py_TYPE(iter)->tp_as_async != NULL && 
Py_TYPE(iter)->tp_as_async->am_send != NULL).

Py_TPFLAGS_HAVE_VERSION_TAG and Py_TPFLAGS_HAVE_FINALIZE are there since 2.6 
and 3.8 respectively, and mentioned in documentation. Extensions that use the 
stable ABI can *check for them*. We cannot do a survey of all existing 
extension modules. The flags can't be removed without breaking stable ABI.

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[issue42747] Remove Py_TPFLAGS_HAVE_VERSION_TAG flag?

[hai shi]

hai shi  added the comment:

>I don't see the purpose of the Py_TPFLAGS_HAVE_VERSION_TAG flag.

IMO, There have no more exact description of `Py_TPFLAGS_HAVE_VERSION_TAG`in 
docs, so I perfer to remove it.

> By the way, is it worth it to remove Py_TPFLAGS_HAVE_FINALIZE? Or is it going 
> to break too many extension modules?

I am not found who use Py_TPFLAGS_HAVE_AM_SEND or Py_TPFLAGS_HAVE_FINALIZE in 
github.I perfer to keep it as soon as posssible if there have users using them.
MAYBE we should do some surveys firstly?

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[issue42747] Remove Py_TPFLAGS_HAVE_VERSION_TAG flag?

[STINNER Victor]

STINNER Victor  added the comment:

Maybe we can keep the constants but define them as 0 and deprecate them.

The question is more if these constants solve a real ABI issue or not.

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[issue42747] Remove Py_TPFLAGS_HAVE_VERSION_TAG flag?

[Dong-hee Na]

Dong-hee Na  added the comment:

Let's emit the deprecated message if Py_TPFLAGS_HAVE_VERSION_TAG is set ;)
For example, PyType_Ready looks like a good place

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[issue42747] Remove Py_TPFLAGS_HAVE_VERSION_TAG flag?

[STINNER Victor]

New submission from STINNER Victor :

Since the PyTypeObject structure is excluded from the limited C API and the 
stable ABI on purpose (PEP 384), I don't see the purpose of the 
Py_TPFLAGS_HAVE_VERSION_TAG flag.

Moreover, a new flag was added recently:

#if !defined(Py_LIMITED_API) || Py_LIMITED_API+0 >= 0x030A
/* Type has am_send entry in tp_as_async slot */
#define Py_TPFLAGS_HAVE_AM_SEND (1UL << 21)
#endif

Should it be also removed?


For example, Py_TPFLAGS_HAVE_FINALIZE was deprecated in bpo-32388 by:

commit ada319bb6d0ebcc68d3e0ef2b4279ea061877ac8
Author: Antoine Pitrou 
Date:   Wed May 29 22:12:38 2019 +0200

bpo-32388: Remove cross-version binary compatibility requirement in 
tp_flags (GH-4944)

It is now allowed to add new fields at the end of the PyTypeObject struct 
without having to allocate a dedicated compatibility flag i
n tp_flags.

This will reduce the risk of running out of bits in the 32-bit tp_flags 
value.


By the way, is it worth it to remove Py_TPFLAGS_HAVE_FINALIZE? Or is it going 
to break too many extension modules?

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components: C API
messages: 383782
nosy: petr.viktorin, pitrou, vstinner
priority: normal
severity: normal
status: open
title: Remove Py_TPFLAGS_HAVE_VERSION_TAG flag?
versions: Python 3.10

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