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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 update_time(self):
 """Retrieve the timestamp at which the variable was updated. See https://cloud.google.com/deployment-manager/runtime-configurator/reference/rest/v1beta1/projects.configs.variables Returns: :class:`~api_core.datetime_helpers.DatetimeWithNanoseconds`, :class:`datetime.datetime` or ``NoneType``: Datetime object parsed from RFC3339 valid timestamp, or ``None`` if the property is not set locally. Raises: ValueError: if value is not a valid RFC3339 timestamp """

        value = self._properties.get("updateTime")
        if value is not None:
            try:
                value = datetime.datetime.strptime(
                    value, datetime_helpers._RFC3339_MICROS
                )
            except ValueError:
                DatetimeNS = datetime_helpers.DatetimeWithNanoseconds
                value = DatetimeNS.from_rfc3339(value)
            naive = value.tzinfo is None or value.tzinfo.utcoffset(value) is None
            if naive:
                value = pytz.utc.localize(value)
        return value