nl: dest as a string 'no_obsolete', default as boolean False and help as a string "Remove obsolete message strings.". call the method parser.add_argument with 5 arguments: string '--keep-pot', action as a string 'store_true',
code: parser . add_argument ( '--keep-pot' , action = 'store_true' , dest = 'keep_pot' , default = False , help = "Keep .pot file after making messages. Useful when debugging." )