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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def get_rfc3339(when):
 """Return an RFC 3339 timestamp. :param datetime.datetime when: a datetime in UTC :return: RFC 3339 timestamp :rtype: str """

    microseconds = format(when.microsecond, '04d')[:4]
    rfc3339 = '%Y-%m-%dT%H:%M:%S.{}Z'
    return when.strftime(rfc3339.format(microseconds))