'warning_once(message, *args, **kwargs)
Logs a warning message.  The same message is never printed again.'

def warning_once(self, message, *args, **kwargs):

    m = (message % args)
    if (m not in self._one_time_warnings):
        if self.isEnabledFor(logging.INFO):
            self._one_time_warnings.add(m)
        self._log(logging.WARNING, message, args, kwargs, 'warning_once')
