switched to using classutil.open_shelve() to take advantage of btree shelve file format
switched to using classutil.open_shelve() to take advantage of btree shelve file format

theoryno3/pygr,RitwikGupta/pygr,ctb/pygr,theoryno3/pygr,RitwikGupta/pygr,GenDataPro/pygr,cjlee112/pygr,ctb/pygr,theoryno3/pygr,ctb/pygr,ctb/pygr,ctb/pygr,cjlee112/pygr,GenDataPro/pygr,RitwikGupta/pygr,cjlee112/pygr,GenDataPro/pygr,cjlee112/pygr