modified open_shelve() to use new dbfile.BtreeShelf class. Also added support for allowReadOnly mode, which will handle write-permission errors by attempting to open the shelve in mode 'r' Now uses exceptions defined in dbfile to report errors; they are all subclasses of IOError.
modified open_shelve() to use new dbfile.BtreeShelf class.
Also added support for allowReadOnly mode, which will handle write-permission
errors by attempting to open the shelve in mode 'r'
Now uses exceptions defined in dbfile to report errors; they are all subclasses
of IOError.

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