[issue39762] PyLong_AS_LONG missing from longobject.h

[Petr Viktorin]

Petr Viktorin  added the comment:

No, in Python 2 the PyInt object (`int` in Python 2) always did fit into a C 
long -- that was the underlying storage. If it didn't fit, a PyLong object 
(`long` in Python 2) was used.

Python 3 doesn't have PyInt, it only has PyLong (`int` in Python 3).

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[issue39762] PyLong_AS_LONG missing from longobject.h

[Enji Cooper]

Enji Cooper  added the comment:

> The reason why there was the PyInt_AS_LONG macro is that it is very simple 
> and efficient. It never fails, because the value of the int object always 
> fits in the C long. PyInt_AsLong is much slower. If you know that the object 
> is int, you can use PyInt_AS_LONG for performance and simplicity.

Another note: this assertion holds generally true with contemporary hardware 
architectures (sizeof(long long) != sizeof(int)), but there are still 32-bit 
hardware/software architectures (ex: non-ARM64 capable ARM arches, i386, 
powerpc 32-bit, etc) that violate this constraint. 32-bit architectures are at 
risk of overflow with 32-bit values.

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[issue39762] PyLong_AS_LONG missing from longobject.h

[Enji Cooper]

Enji Cooper  added the comment:

PyInt_AS_LONG doesn't exist on python 3, however:

$ grep -r PyInt_AS_LONG /usr/include/
[/usr/include/python2.7/intobject.h:#define PyInt_AS_LONG(op) (((PyIntObject 
*)(op))->ob_ival)

The code smell for the pieces that use PyInt_AS_LONG seems a bit questionable 
since they're used as array indexes; I'll poke a bit more and look at using one 
of the other sets of C APIs instead in our project.

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[issue39762] PyLong_AS_LONG missing from longobject.h

[Serhiy Storchaka]

Serhiy Storchaka  added the comment:

The reason why there was the PyInt_AS_LONG macro is that it is very simple and 
efficient. It never fails, because the value of the int object always fits in 
the C long. PyInt_AsLong is much slower. If you know that the object is int, 
you can use PyInt_AS_LONG for performance and simplicity.

In contrary, converting the long object to the C long value requires a loop and 
it can overflow. There is no reason to implement it as a macro. You can use the 
PyLong_AsLong function.

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[issue39762] PyLong_AS_LONG missing from longobject.h

[Enji Cooper]

Enji Cooper  added the comment:

@serhiy.storchaka: understood. Figured this would be a good errata note for 
others to potentially find in the future.

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[issue39762] PyLong_AS_LONG missing from longobject.h

[Serhiy Storchaka]

Serhiy Storchaka  added the comment:

Python 2 is no longer supported.

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nosy: +serhiy.storchaka
resolution:  -> out of date
stage:  -> resolved
status: open -> closed

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[issue39762] PyLong_AS_LONG missing from longobject.h

[Enji Cooper]

Enji Cooper  added the comment:

Workaround PR posted here: https://github.com/encukou/py3c/pull/28

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[issue39762] PyLong_AS_LONG missing from longobject.h

[Enji Cooper]

Enji Cooper  added the comment:

For the record, this seems like it might be the only discrepancy, per the py3c 
project's exported PyInt APIs:

$ for api in `awk '$2 ~ /^PyInt/ { print $3 }' include/py3c/compat.h`; do grep 
-q $api /usr/include/python2.7/longobject.h || echo $api; done
PyLong_AS_LONG

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[issue39762] PyLong_AS_LONG missing from longobject.h

[Enji Cooper]

Enji Cooper  added the comment:

For the record, some projects (like Cython, pywin32) worked around this by 
adding a preprocessor alias, PyLong_AS_LONG -> PyInt_AS_LONG with python 2.x.

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[issue39762] PyLong_AS_LONG missing from longobject.h

[Enji Cooper]

New submission from Enji Cooper :

While trying to port python 2 C extension code forward to python 3, I noticed 
that the python 2.6 PyInt -> PyLong unification lacks a forward-compatible API 
for PyLong_AS_LONG.

I'm not sure if this was intentional, but it is a slightly annoying wicket to 
deal with when forward C extension code that needs to straddle 2 and 3 for a 
period of time.

--
components: C API
messages: 362705
nosy: ngie
priority: normal
severity: normal
status: open
title: PyLong_AS_LONG missing from longobject.h
versions: Python 2.7

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