default='', type="str", action='callback', callback=optparse_listvalue_callback)
parser.add_option ('-X','--extra',dest='extras',default={},type='str',metavar="<EXTRA_ASSIGNS>",
action="callback", callback=optparse_dictvalue_callback, nargs=1,
default='', type="str", action='callback', callback=optparse_listvalue_callback)
parser.add_option ('-X','--extra',dest='extras',default={},type='str',metavar="<EXTRA_ASSIGNS>",
action="callback", callback=optparse_dictvalue_callback, nargs=1,