Sorry for the long delay in answering this issue: ctypes and libffi issues do not get a lot of attention currently. I assume you must have long ago found a solution to the problem but, just for the record and assuming I understand the problem correctly, if you build Python on centos6 with its default libffi.so.5 and then try to move those binaries to a centos7 system that does not include a libffi.so.5 along with libffi.so.6, you are out of luck.  Normally, the change from .5 to .6 would indicate some ABI incompatibility between the two libffi versions. Rebuilding Python on centos7 should produce a working Python that links with the latest library versions, including libffi, available on that centos release.