docs: def datetime_to_httpdate(dt):
      """Convert datetime.datetime or Unix timestamp to HTTP date."""
      if isinstance(dt, (int, float)):
          return format_date_time(dt)
      elif isinstance(dt, datetime):
          return format_date_time(datetime_to_timestamp(dt))
      else:
          raise TypeError("expected datetime.datetime or timestamp (int/float),"
                          " got '%s'" % dt)