code: def rfc1123_date(timestamp=None):
      
      if timestamp is None:
          timestamp = time.time()
      timestamp = int(timestamp)
      global _cached_timestamp, _cached_datestring
      if timestamp != _cached_timestamp:
          # The time stamp must be GMT, and cannot be localized.
          tm = time.gmtime(timestamp)
          s = rfc1123_fmt.replace('%a', weekdays[tm.tm_wday]) \
                         .replace('%b', months[tm.tm_mon-1])
          _cached_datestring = time.strftime(s, tm)
          _cached_timestamp = timestamp
      return _cached_datestring
docs: Create a RFC1123 style Date header for *timestamp*.