On HP-UX, python can no longer find extension modules with the '.sl' suffix.

[fspatar@hpux1131:/cust/fspatar/buildtest/hp-ux/11.31/build]> ~/tmp/investigation3/old/bin/python3
Python 3.8.11 (default, Aug  3 2021, 06:15:31) 
[GCC 4.2.4] on hp-ux-pa
Type "help", "copyright", "credits" or "license" for more information.
>>> import M2Crypto
Traceback (most recent call last):
  File "/cust/fspatar/buildtest/hp-ux/11.31/build/M2Crypto/m2crypto.py", line 16, in swig_import_helper
    fp, pathname, description = imp.find_module('_m2crypto', [dirname(__file__)])
  File "/h/fspatar/tmp/investigation3/old/lib/python3.8/imp.py", line 296, in find_module
    raise ImportError(_ERR_MSG.format(name), name=name)
ImportError: No module named '_m2crypto'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/cust/fspatar/buildtest/hp-ux/11.31/build/M2Crypto/__init__.py", line 37, in <module>
    from M2Crypto import (ASN1, AuthCookie, BIO, BN, DH, DSA, EVP, Engine, Err,
  File "/cust/fspatar/buildtest/hp-ux/11.31/build/M2Crypto/ASN1.py", line 15, in <module>
    from M2Crypto import BIO, m2, py27plus, six, has_typing
  File "/cust/fspatar/buildtest/hp-ux/11.31/build/M2Crypto/BIO.py", line 9, in <module>
    from M2Crypto import m2, py27plus, six, has_typing
  File "/cust/fspatar/buildtest/hp-ux/11.31/build/M2Crypto/m2.py", line 30, in <module>
    from M2Crypto.m2crypto import *
  File "/cust/fspatar/buildtest/hp-ux/11.31/build/M2Crypto/m2crypto.py", line 26, in <module>
    _m2crypto = swig_import_helper()
  File "/cust/fspatar/buildtest/hp-ux/11.31/build/M2Crypto/m2crypto.py", line 18, in swig_import_helper
    import _m2crypto
ModuleNotFoundError: No module named '_m2crypto'

This works fine in python 3.8.5

[fspatar@hpux1131:/cust/fspatar/buildtest/hp-ux/11.31/build]> /opt/OPSWbuildtools/2.0.5/python/3.8.5.04/bin/python3
Python 3.8.5 (default, Jul 28 2021, 08:38:55) 
[GCC 4.2.4] on hp-ux-pa
Type "help", "copyright", "credits" or "license" for more information.
>>> import M2Crypto

It seems to be related to recent changes from https://bugs.python.org/issue42604

Given the file name is _m2crypto.sl, python 3.8.11 can no longer find it. Based on https://www.python.org/dev/peps/pep-3149/#pep-384, my understanding is that python should search for the following file names when extension module _m2crypto is imported (in this order):

_m2crypto.cpython-38.sl
_m2crypto.so

Python can only load the extension module if the file name is _m2crypto.cpython-38.sl

[fspatar@hpux1131:/cust/fspatar/buildtest/hp-ux/11.31/build]> ~/tmp/investigation3/old/bin/python3
Python 3.8.11 (default, Aug  3 2021, 06:15:31) 
[GCC 4.2.4] on hp-ux-pa
Type "help", "copyright", "credits" or "license" for more information.
>>> import _imp
>>> _imp.extension_suffixes()
['.cpython-38.sl']
>>> 

[fspatar@hpux1131:/cust/fspatar/buildtest/hp-ux/11.31/build]> /opt/OPSWbuildtools/2.0.5/python/3.8.5.04/bin/python3
Python 3.8.5 (default, Jul 28 2021, 08:38:55) 
[GCC 4.2.4] on hp-ux-pa
Type "help", "copyright", "credits" or "license" for more information.
>>> import _imp
>>> _imp.extension_suffixes()
['.sl']
>>>

Can you please try to convert your patch into a GitHub pull request?

I assume you tried and succeeded with your patch. Could you post what `_imp.extension_suffixes()` reports after the patch? 

I am a bit confused because you said the following, should the last line be `_m2crypto.sl` and not `_m2crypto.sl` ?

my understanding is that python should search for the following file names when extension module _m2crypto is imported (in this order):

_m2crypto.cpython-38.sl
_m2crypto.so

@mattip
Yes, the patch fixed the issue and the extension module import works.

With the patch applied:

[fspatar@hpux1131:/cust/fspatar/buildtest/hp-ux/11.31/build]> /opt/OPSWbuildtools/2.0.5/python/3.8.11.01/bin/python3
Python 3.8.11 (default, Aug  4 2021, 03:13:01) 
[GCC 4.2.4] on hp-ux-pa
Type "help", "copyright", "credits" or "license" for more information.
>>> import _imp
>>> _imp.extension_suffixes()
['.cpython-38.sl', '.sl']
>>> 

Sorry for the confusion; I meant python should search for the following file names when extension module _m2crypto is imported (in this order):

_m2crypto.cpython-38.sl
_m2crypto.sl

@vstinner
I'm working on the pull request.

New changeset 2396fa6537d79554ac694dbd2b0b30eeb3476c80 by Florin Spătar in branch 'main':
bpo-44959: Add fallback to extension modules with '.sl' suffix on HP-UX (GH-27857)
https://github.com/python/cpython/commit/2396fa6537d79554ac694dbd2b0b30eeb3476c80

Can this be merged to python 3.10 as well? Thanks

> Can this be merged to python 3.10 as well? Thanks

It's unclear to me if it's a new feature or a bugfix. But since the change is trivial, I'm fine with backporting it as a bugfix to 3.9 and 3.10 branches.

New changeset aa8c3446c085175e65e736b0d2e32719c00004d2 by Miss Islington (bot) in branch '3.9':
bpo-44959: Add fallback to extension modules with '.sl' suffix on HP-UX (GH-27857)
https://github.com/python/cpython/commit/aa8c3446c085175e65e736b0d2e32719c00004d2

New changeset 6d66de97f814fb504296c153957d87e49993f8ec by Miss Islington (bot) in branch '3.10':
bpo-44959: Add fallback to extension modules with '.sl' suffix on HP-UX (GH-27857) (GH-29152)
https://github.com/python/cpython/commit/6d66de97f814fb504296c153957d87e49993f8ec