Fixed error on Python 2
Fixed error on Python 2

miaecle/deepchem,lilleswing/deepchem,miaecle/deepchem,Agent007/deepchem,deepchem/deepchem,lilleswing/deepchem,deepchem/deepchem,ktaneishi/deepchem,peastman/deepchem,Agent007/deepchem,peastman/deepchem,miaecle/deepchem,ktaneishi/deepchem,lilleswing/deepchem,ktaneishi/deepchem,Agent007/deepchem