The find_library_function() in Lib/distutils/unixccompiler.py does a very simple-minded check to determine the existence of a library. It basically only checks that a certain .so file exists. This may lead to false positives: the mere existence of a .so file does not imply that we can actually link against that library.

In addition to (or even better: instead of) checking the existence of the file, you should try to (in the spirit of autoconf) compile a simple program using $CC -l$LIB prog.c -o prog

One particular instance of where things can go wrong is with a 32-bit/64-bit multilib installation. Python might find a 64-bit library in /usr/lib when we're actually compiling 32-bit with libraries in /usr/lib32.

Hi Jeroen, thanks for the report.  Did you run into this while building a distribution or did you find it just reading the code?  Distutils is in a special state where we only fix bugs but don’t do any improvement for the sake of improvements, because many setup.py scripts rely on undocumented details.

Sorry for the late answer, but yes: I found this out using an actual compilation.  I must admit it was in a bit of an usual situation (32-bit userspace on a mixed 32/64-bit mutilib installation), but most other software packages have no problems configuring correctly in such a situation.

I can imagine that it's not a trivial change and would require some redesign.

Some more context: this was discovered when building Python as part of Sage, see http://trac.sagemath.org/sage_trac/ticket/12725 for the downstream bug report.

Distutils is now deprecated (see PEP 632) and all tagged issues are being closed. From now until removal, only release blocking issues will be considered for distutils.

If this issue does not relate to distutils, please remove the component and reopen it. If you believe it still requires a fix, most likely the issue should be re-reported at https://github.com/pypa/setuptools