return log in unicode

def format(self, record):
        """
        return log in unicode
        """
        self._format_record(record)

        record_dict = {}
        for k, v in record.__dict__.items():
            if isinstance(k, str):
                k = decode_(k, 'utf8')
            if isinstance(v, str):
                v = decode_(v, 'utf8', 'replace')
            record_dict[k] = v

        if 'color' in self.fmt or 'end_color' in self.fmt:
            record_dict['color'], record_dict['end_color'] = _color(record.levelno)

        log = self.ufmt % record_dict

        if record.exc_text:
            if log[-1:] != '\n':
                log += '\n'
            log += decode_(record.exc_text, 'utf8', 'replace')

        log = log.replace('\n', '\n' + self.tab)

        return log