python-abi-hack.md

Properly resolving versioned Python shared object suffixes

So, the other day I was trying to call a C library from a Python script using ctypes.cdll.LoadLibrary, and the funniest thing happened: it didn't work properly across multiple Python interpreter versions. At this point I usually turn the the PEP documents, and found this in PEP3149:

The following information MUST be included in the shared library file name: The Python implementation (e.g. cpython, pypy, jython, etc.) The interpreter's major and minor version numbers

So, how do we get this information? The PEP document stops short of telling us. However, I gathered a few bits of information along the way to finding out:

1. Python 2.6-3.1 do not implement this, so these version need no special suffix
2. Python >3.1 implements a .cpython-vv.so suffix where vv is major/minor version number
3. PyPy does something different.

The following code snippet is what I came up with for determining the suffix for the compiled shared library.

import sys

try:
    from sysconfig import get_config_var as get
    # https://mail.gnome.org/archives/commits-list/2013-April/msg05415.html
    # https://www.python.org/dev/peps/pep-3149/
    SUFFIX = get('EXT_SUFFIX') or get('SO') or '.so'
except ImportError:
    SUFFIX = '.so'

# Check for pypy interpreter
if hasattr(sys, 'pypy_version_info'):
    if sys.version_info.major == 2:
        SUFFIX = ".pypy-{0}{1}.so".format(sys.pypy_version_info.major, sys.pypy_version_info.minor)
    elif sys.version_info.major == 3:
        SUFFIX = ".pypy3-{0}{1}.so".format(sys.pypy_version_info.major, sys.pypy_version_info.minor)