'Specify the format to display tracebacks with. Valid formats are
\'plain\', \'emacs\', and \'cgitb\' which uses the nicely verbose stdlib
cgitb.text function'

def opt_tbformat(self, opt):

    try:
        self['tbformat'] = TBFORMAT_MAP[opt]
    except KeyError:
        raise usage.UsageError("tbformat    must    be    'plain',    'emacs',    or    'cgitb'.")
