docs: def add_db_arguments(parser, db_option=False):
      """Adds common arguments for the database sub-commands to
      `parser`.
  
      `db_option` provides a means to work around
      https://bugs.python.org/issue9338 whereby a positional argument
      that follows an optional argument with nargs='+' will not be
      recognised. When `db_optional` is True, create the database
      argument as a required optional argument, rather than a positional
      argument.
  
      """
      parser.add_argument('-m', '--memory', action='store_true',
                          help=constants.DB_MEMORY_HELP)
      parser.add_argument('-r', '--ram', default=3, help=constants.DB_RAM_HELP,
                          type=int)
      if db_option:
          parser.add_argument('-d', '--db', help=constants.DB_DATABASE_HELP,
                              metavar='DATABASE', required=True)
      else:
          parser.add_argument('db', help=constants.DB_DATABASE_HELP,
                              metavar='DATABASE')