code: def get_rfc3339(when):
      
      microseconds = format(when.microsecond, '04d')[:4]
      rfc3339 = '%Y-%m-%dT%H:%M:%S.{}Z'
      return when.strftime(rfc3339.format(microseconds))
docs: Return an RFC 3339 timestamp.
  
      :param datetime.datetime when: a datetime in UTC
      :return: RFC 3339 timestamp
      :rtype: str