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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 _client(self, key_id):
 """Returns a Boto3 KMS client for the appropriate region. :param str key_id: KMS CMK ID """

        region_name = _region_from_key_id(key_id, self.default_region)
        self.add_regional_client(region_name)
        return self._regional_clients[region_name]