docs: def command_line():
      '''
      Parses users command line arguments and returns the namespace
      containing parsed values.
      '''
      description = 'Kan helps you find the book'
      version     = ' '.join([__version__, __release__])
      parser      = ArgumentParser(prog='kan', description=description)
  
      subparser   = parser.add_subparsers(help='Search by')
  
      by_title    = subparser.add_parser('title', help='Book title',)
      by_title.add_argument('title', help='Book name')
  
      by_isbn     = subparser.add_parser('isbn', help='ISBN code')
      by_isbn.add_argument('code', help='Valid ISBN code')
  
      by_author   = subparser.add_parser('author', help='Book author')
      by_author.add_argument('author', help='Authors name')
      by_author.add_argument('--recent', help='Search by most recent', action='store_true')
      by_author.add_argument('--top', help='Search by best selling', action='store_true')
  
      # Main Parser
      parser.add_argument(
          '-v', '--version', action='version',
          version="%s v%s" % ('kan', version),
      )
      parser.add_argument(
          '--title',
          help='Title of the book',
          metavar='name',
      )
      parser.add_argument(
          '--author',
          default=None,
          metavar='name',
          help='Name of the author',
      )
      parser.add_argument(
          '--subject',
          type=str,
          help='Specify subject matter by category',
          metavar='topic',
      )
      parser.add_argument(
          '--max',
          type=int,
          metavar='n',
          default=3,
          choices=range(41),
          help='Maximum results to get per query: default=3, max=40',
      )
      parser.add_argument(
          '--language',
          type=str,
          metavar='code',
          default='',
          help='Restrict the search results to those with a certain language code',
      )
      parser.add_argument(
          '--verbose',
          action='store_true',
          help='Print out debug information',
      )
  
      return parser.parse_args()