code: def timestamp_with_tzinfo(dt):
      
      utc = tzutc()
  
      if dt.tzinfo:
          dt = dt.astimezone(utc).replace(tzinfo=None)
      return dt.isoformat() + 'Z'
docs: Serialize a date/time value into an ISO8601 text representation
      adjusted (if needed) to UTC timezone.
  
      For instance:
      >>> serialize_date(datetime(2012, 4, 10, 22, 38, 20, 604391))
      '2012-04-10T22:38:20.604391Z'