'Log file format.
(options: "text", "json"; default: "text" if the log file is a tty,
otherwise "json")'

def opt_log_format(self, format):

    format = format.lower()
    if (format == 'text'):
        self['fileLogObserverFactory'] = textFileLogObserver
    elif (format == 'json'):
        self['fileLogObserverFactory'] = jsonFileLogObserver
    else:
        raise UsageError('Invalid    log    format:    {}'.format(format))
    self['logFormat'] = format
