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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_ituz(self, callsign, timestamp=timestamp_now):
 """ Returns ITU Zone of a callsign Args: callsign (str):
 Amateur Radio callsign timestamp (datetime, optional):
 datetime in UTC (tzinfo=pytz.UTC) Returns: int: containing the callsign's CQ Zone Raises: KeyError: No ITU Zone found for callsign Note: Currently, only Country-files.com lookup database contains ITU Zones """

        return self.get_all(callsign, timestamp)[const.ITUZ]