The issue with confliciting expat versions has poped up again in python 3.
http://bugs.python.org/issue1295808

It looks like the fix for this was removed when upgrading to expat 2.1 in http://hg.python.org/cpython/rev/e4dc8be9a72f      on Sat, 14 Jul 2012 14:12:35 -0700 Gregory P. Smith
--- a/Modules/expat/expat_external.h
/* Namespace external symbols to allow multiple libexpat version to
-   co-exist. */
-#include "pyexpatns.h"

Same backtrace as before.
#0  0x0000003507481321 in __strlen_sse2 () from /lib64/libc.so.6
#1  0x00007facace1b0d0 in PyUnicode_FromString (u=0x0) at Objects/unicodeobject.c:1824
#2  0x00007facaceefddc in PyModule_AddStringConstant (m=0x7fac9c7cf678,
    name=0x7fac9c5ab2e3 "XML_ERROR_UNBOUND_PREFIX", value=0x0) at Python/modsupport.c:554
#3  0x00007fac9c582f31 in PyInit_pyexpat () at /home/hex/Downloads/Python-3.Modules/pyexpat.c:1870
#4  0x00007facacee8f89 in _PyImport_LoadDynamicModule (name=0x7fac9c7db450, path=0x7fac9cdf9928, fp=0x0)