Fix operator test for python3
Fix operator test for python3

thewtex/tomviz,cjh1/tomviz,cjh1/tomviz,mathturtle/tomviz,OpenChemistry/tomviz,mathturtle/tomviz,OpenChemistry/tomviz,cryos/tomviz,thewtex/tomviz,cryos/tomviz,cjh1/tomviz,thewtex/tomviz,cryos/tomviz,OpenChemistry/tomviz,OpenChemistry/tomviz,mathturtle/tomviz