fix transformer API in Python
fix transformer API in Python

simonellistonball/magellan,harsha2010/magellan,YanjieGao/magellan,simonellistonball/magellan,kcompher/magellan,andrewor14/magellan,kcompher/magellan,YanjieGao/magellan,andrewor14/magellan,harsha2010/magellan