code: def _(obj):
      
  
      tz_offset = obj.utcoffset()
  
      if not tz_offset or tz_offset == UTC_ZERO:
          iso_datetime = obj.strftime('%Y-%m-%dT%H:%M:%S.%fZ')
      else:
          iso_datetime = obj.isoformat()
  
      return iso_datetime
docs: ISO 8601 format. Interprets naive datetime as UTC with zulu suffix.