Python dl_open() function (from dl module) calls dlopen() and check 
its result: if it's NULL, it's an error. This is correct if I read the 
man page. But with an invalid flag value (-1), dlopen() returns NULL 
but dlerror() also gives a NULL pointer. Example:

>>> import dl
>>> dl.open("/usr/lib/libm.so", -1)
Erreur de segmentation (core dumped)

Workaround: use a static error message if dlerror() returns NULL.

I wrote a patch for dl_open() but other functions (in ctypes module?) 
should also call dlerror().

As expected, the bug can be reproduced with ctypes.dlopen(). 
py_dl_open() function of Modules/_ctypes/callproc.c should be merged 
with Modules/dlmodule.c.

Here use at least the attached patch for ctypes (same job than the 
other patch: use default string if dlerror() returns NULL).

I can confirm the problem on ubuntu linux.

Thanks for the patch, fixed in trunk rev 64977 and py3k rev 64978.