'Return the current date and time formatted for a message header.'

def date_time_string(self, timestamp=None):

    if (timestamp is None):
        timestamp = time.time()
    (year, month, day, hh, mm, ss, wd, y, z) = time.gmtime(timestamp)
    s = ('%s,    %02d    %3s    %4d    %02d:%02d:%02d    GMT' % (self.weekdayname[wd], day, self.monthname[month], year, hh, mm, ss))
    return s
