demandimport: disable lazy import of __builtin__ Demandimport uses the "try to import __builtin__, else use builtins" trick to handle Python 3. External libraries and extensions might do something similar. On Fedora 25 subversion-python-1.9.4-4.fc25.x86_64 will do just that (except the opposite) ... and it failed all subversion convert tests because demandimport was hiding that it didn't have builtins but should use __builtin__. The builtin module has already been imported when demandimport is loaded so there is no point in trying to import it on demand. Just always ignore both variants in demandimport.