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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 publish_proto_metadata_update(self):
 """ Publish protobuf model in ipfs and update existing metadata file """

        metadata = load_mpe_service_metadata(self.args.metadata_file)
        ipfs_hash_base58 = utils_ipfs.publish_proto_in_ipfs(self._get_ipfs_client(), self.args.protodir)
        metadata.set_simple_field("model_ipfs_hash", ipfs_hash_base58)
        metadata.save_pretty(self.args.metadata_file)