Last night I was trying to check whether blockJobInfo() method will raise an error when it returns 'None' in v1.2.5 libvirt Python bindings. (Eric Blake confirmed on IRC: "the python bindings have, as a general rule, always raised a libvirtError if the C binding code returns None"). Before asking on IRC, I built the bindings and the below is what I noticed. Let's first see what's in current Git master: $ less build/libvirt.py [...] def blockJobInfo(self, path, flags=0): """Get progress information for a block job """ ret = libvirtmod.virDomainGetBlockJobInfo(self._o, path, flags) if ret is None: raise libvirtError ('virDomainGetBlockJobInfo() failed', dom=self) return ret [...] Now try to find out what is present in v1.2.5 by quickly building the bindings for that tag: $ git checkout v1.2.5 $ python setup.py build Hmm, once built, there's no blockJobInfo() method in build/libvirt.py! (When I mentioned this on #virt, OFTC, Cole confirmed he could reproduce the behavior, too. Not sure if it's a regression in v1.2.5.) However, the libvirt "glue code" for libvirt_virDomainGetBlockJobInfo() exists in libvirt-python/libvirt-override.c, so checking there (again, for v1.2.5), we see: 4755 if (c_ret == 0) { 4756 return dict; 4757 } else if (c_ret < 0) { 4758 Py_DECREF(dict); 4759 return VIR_PY_NONE; 4760 } IIUC, the VIR_PY_NONE means it raises an exception (libvirtError). -- /kashyap