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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 exists(self):
 """Test whether this instance exists. See https://cloud.google.com/spanner/reference/rpc/google.spanner.admin.instance.v1#google.spanner.admin.instance.v1.InstanceAdmin.GetInstanceConfig :rtype: bool :returns: True if the instance exists, else false """

        api = self._client.instance_admin_api
        metadata = _metadata_with_prefix(self.name)

        try:
            api.get_instance(self.name, metadata=metadata)
        except NotFound:
            return False

        return True