pip._internal.utils.glibc_version_string() can use os.confstr('CS_GNU_LIBC_VERSION') to avoid ctypes

[vstinner]

Currently, the pip._internal.utils.glibc_version_string() function is implemented with ctypes to access gnu_get_libc_version() function. But os.confstr('CS_GNU_LIBC_VERSION') could be used instead to avoid ctypes.

I recently modified platform.libc_ver() on Python stdlib to use os.confstr('CS_GNU_LIBC_VERSION') is available:

• https://bugs.python.org/issue35389
• https://github.com/python/cpython/blob/d4efd917ac24940063a1ce80073fe3570c5f07f8/Lib/platform.py#L174-L183

    if executable is None:
        try:
            ver = os.confstr('CS_GNU_LIBC_VERSION')
            # parse 'glibc 2.28' as ('glibc', '2.28')
            parts = ver.split(maxsplit=1)
            if len(parts) == 2:
                return tuple(parts)
        except (AttributeError, ValueError, OSError):
            # os.confstr() or CS_GNU_LIBC_VERSION value not available
            pass

Note: I noticed this issue when an user reported a traceback in pip when the ctypes is not available: https://mail.python.org/archives/list/python-dev@python.org/thread/MTIRNYFAZTQQPHKAQXXREP33NYV2TW2J/

[pradyunsg]

Thanks for filing this @vstinner!

---

If anyone wants to tackle this and file a PR, that'd be awesome!

[cjerdonek]

How does this impact PR #6544 / issue #6543?

[vstinner]

How does this impact PR #6544 / issue #6543?

The best would be if pip could avoid completely ctypes, but I'm not sure if it's possible. In the past, I reported issues times to times when pip broke when ctypes was not available, but it seems to be a lost battle: pip or pip dependencies commonly use ctypes. Instead, on the Python upstream CI, we now try to ensure that ctypes is always available on buildbots.

If you want to test a Python without ctypes, inject this code before using pip:

import sys
sys.modules['_ctypes'] = None
sys.modules['ctypes'] = None

[brandtbucher]

I'm putting together a PR for this based on the usage of os.confstr above.