parser.set_defaults(operation="and",)
parser.add_option("", "--operation", dest="operation", metavar="and",
help="""Which operation to perform on the two sets. (and, or, minus""")
parser.set_defaults(operation="and",)
parser.add_option("", "--operation", dest="operation", metavar="and",
help="""Which operation to perform on the two sets. (and, or, minus""")