[issue41078] [C API] Convert PyTuple_GET_ITEM() macro to a static inline function

[STINNER Victor]

STINNER Victor  added the comment:

The PEP 620 is still a draft. I prefer to work on other C API changes before 
coming back to this change which may break many C extensions. I failed finding 
time to design an API to expose a PyObject** array "view" with a function to 
release/destroy the view.

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

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[issue41078] [C API] Convert PyTuple_GET_ITEM() macro to a static inline function

[STINNER Victor]

STINNER Victor  added the comment:

See "(PEP 620) C API for efficient loop iterating on a sequence of PyObject** 
or other C types" thread on python-dev:
https://mail.python.org/archives/list/python-...@python.org/thread/632CV42376SWVYAZTHG4ROOV2HRHOVZ7/

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[issue41078] [C API] Convert PyTuple_GET_ITEM() macro to a static inline function

[STINNER Victor]

STINNER Victor  added the comment:

I suggest you to discuss the PEP 620 on python-dev, rather than on the bug 
tracker. I just posted it there today.

This issue tracks the implemetation of one part of the PEP 620.

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[issue41078] [C API] Convert PyTuple_GET_ITEM() macro to a static inline function

[Stefan Behnel]

Stefan Behnel  added the comment:

> Also, later, these structures may change to be more efficient.

Tuples? Really?

Ok, quoting PEP-620:
> Members of … PyTupleObject structures have not changed since the "Initial 
> revision" commit (1990)

I honestly think the reason for that might simply be that there's not so much 
to improve for tuples.

> nothing prevents a C extension to get or set directly
> PyTupleObject.ob_item[0] (the first item of a tuple).

I certainly understand that that is a problem, especially if "PyObject" may 
change in the future. And this is essentially what the current 
"PyTuple_GET_ITEM()" macro does in a binary module.

Should we also turn "_PyTuple_ITEMS()" into a public inline function then to 
make up for the loss of the "&PyTuple_GET_ITEM(t, 0)" pattern? It would make it 
explicit what is intended. I think that should be our main goal in the CPython 
side.

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[issue41078] [C API] Convert PyTuple_GET_ITEM() macro to a static inline function

[STINNER Victor]

STINNER Victor  added the comment:

The long rationale is explained in PEP 620:
https://www.python.org/dev/peps/pep-0620/

PyTupleObject and PyListObject structures must become opaque. Also, later, 
these structures may change to be more efficient.

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[issue41078] [C API] Convert PyTuple_GET_ITEM() macro to a static inline function

[Stefan Behnel]

Stefan Behnel  added the comment:

> Giving a direct access to an array or PyObject* (PyObject**) is causing 
> issues with other Python implementations, like PyPy, which don't use PyObject 
> internally.

I'm wondering – if the intention is to help other implementations, then why do 
we need to break extensions in *CPython* for that? In CPython, this usage seems 
perfectly valid with the current data structure. If that ever changes, we can 
still make this change as well, but do you really see the internal layout of 
tuples change at some point? (Lists are a different case, I'd say, but tuples?)

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[issue41078] [C API] Convert PyTuple_GET_ITEM() macro to a static inline function

[STINNER Victor]

STINNER Victor  added the comment:

PySequence_Fast_ITEMS() is used in numpy at 7 lines:

numpy/core/src/common/ufunc_override.c:118:*out_objs = 
PySequence_Fast_ITEMS(seq);

---
PyUFuncOverride_GetOutObjects(PyObject *kwds, PyObject **out_kwd_obj, PyObject 
***out_objs)
---
=> PyObject** is part of the numpy C API (it's even a pointer to a PyObject** 
array)!


numpy/core/src/multiarray/arrayfunction_override.c:80:PyObject **items = 
PySequence_Fast_ITEMS(relevant_args);
---
static int
get_implementing_args_and_methods(PyObject *relevant_args,
  PyObject **implementing_args,
  PyObject **methods)
{
int num_implementing_args = 0;
Py_ssize_t i;
int j;

PyObject **items = PySequence_Fast_ITEMS(relevant_args);
Py_ssize_t length = PySequence_Fast_GET_SIZE(relevant_args);

for (i = 0; i < length; i++) {
int new_class = 1;
PyObject *argument = items[i];


=> here PySequence_Fast_GET_ITEM() can be used instead.


numpy/core/src/multiarray/arrayfunction_override.c:167:PyObject **items = 
PySequence_Fast_ITEMS(types);
numpy/core/src/multiarray/common.c:434:objects = PySequence_Fast_ITEMS(seq);
numpy/core/src/multiarray/iterators.c:1368:ret = multiiter_new_impl(n, 
PySequence_Fast_ITEMS(fast_seq));
numpy/core/src/multiarray/methods.c:1015:in_objs = 
PySequence_Fast_ITEMS(fast);
numpy/core/src/umath/override.c:38:arg_objs = PySequence_Fast_ITEMS(args);

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[issue41078] [C API] Convert PyTuple_GET_ITEM() macro to a static inline function

[STINNER Victor]

STINNER Victor  added the comment:

PySequence_Fast_ITEMS() must also be deprecated since it also gives a direct 
access to PyTupleObject.ob_item and PyListObject.ob_item members (PyObject**). 
PySequence_Fast_GET_ITEM() should be used instead.

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[issue41078] [C API] Convert PyTuple_GET_ITEM() macro to a static inline function

[STINNER Victor]

STINNER Victor  added the comment:

The PR 21059 breaks Cython. I reported the issue to Cython upstream:
https://github.com/cython/cython/issues/3701

numpy is also affected: code generated by Cython (numpy/random/_mt19937.c) 
contains the issue.

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[issue41078] [C API] Convert PyTuple_GET_ITEM() macro to a static inline function

[STINNER Victor]

Change by STINNER Victor :


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pull_request: https://github.com/python/cpython/pull/21059

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[issue41078] [C API] Convert PyTuple_GET_ITEM() macro to a static inline function

[STINNER Victor]

STINNER Victor  added the comment:


New changeset c96d00e88ead8f99bb6aa1357928ac4545d9287c by Victor Stinner in 
branch 'master':
bpo-41078: Fix bltinmodule.c with Py_TRACE_REFS (GH-21058)
https://github.com/python/cpython/commit/c96d00e88ead8f99bb6aa1357928ac4545d9287c


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[issue41078] [C API] Convert PyTuple_GET_ITEM() macro to a static inline function

[STINNER Victor]

Change by STINNER Victor :


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pull_request: https://github.com/python/cpython/pull/21058

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[issue41078] [C API] Convert PyTuple_GET_ITEM() macro to a static inline function

[STINNER Victor]

STINNER Victor  added the comment:


New changeset c45dbe93b7094fe014442c198727ee38b25541c4 by Victor Stinner in 
branch 'master':
bpo-41078: Add pycore_list.h internal header file (GH-21057)
https://github.com/python/cpython/commit/c45dbe93b7094fe014442c198727ee38b25541c4


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[issue41078] [C API] Convert PyTuple_GET_ITEM() macro to a static inline function

[STINNER Victor]

STINNER Victor  added the comment:


New changeset 384621c42f9102e31ba2c47feba144af09c989e5 by Victor Stinner in 
branch 'master':
bpo-41078: Rename pycore_tupleobject.h to pycore_tuple.h (GH-21056)
https://github.com/python/cpython/commit/384621c42f9102e31ba2c47feba144af09c989e5


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[issue41078] [C API] Convert PyTuple_GET_ITEM() macro to a static inline function

[STINNER Victor]

Change by STINNER Victor :


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pull_request: https://github.com/python/cpython/pull/21057

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[issue41078] [C API] Convert PyTuple_GET_ITEM() macro to a static inline function

[STINNER Victor]

Change by STINNER Victor :


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stage:  -> patch review
pull_request: https://github.com/python/cpython/pull/21056

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[issue41078] [C API] Convert PyTuple_GET_ITEM() macro to a static inline function

[STINNER Victor]

New submission from STINNER Victor :

PyTuple_GET_ITEM() can be abused to access directly the PyTupleObject.ob_item 
member:

   PyObject **items = &PyTuple_GET_ITEM(0);

Giving a direct access to an array or PyObject* (PyObject**) is causing issues 
with other Python implementations, like PyPy, which don't use PyObject 
internally.

I propose to convert the PyTuple_GET_ITEM() and PyList_GET_ITEM() macros to 
static inline functions to disallow that.

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components: C API
messages: 372091
nosy: vstinner
priority: normal
severity: normal
status: open
title: [C API] Convert PyTuple_GET_ITEM() macro to a static inline function
versions: Python 3.10

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