code: def get_cache_time_left(expires_header):
      
      epoch = datetime(1970, 1, 1)
      # this date is ALWAYS in UTC (RFC 7231)
      expire = (
          datetime(
              *parsedate(expires_header)[:6]
          ) - epoch
      ).total_seconds()
      now = (datetime.utcnow() - epoch).total_seconds()
      return int(expire) - int(now)
docs: return the time left in second for an expires header