Fixed error on Python 2
Fixed error on Python 2

peastman/deepchem,miaecle/deepchem,lilleswing/deepchem,miaecle/deepchem,deepchem/deepchem,lilleswing/deepchem,deepchem/deepchem,lilleswing/deepchem,miaecle/deepchem,peastman/deepchem