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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 make_optimize_tensor(self, model, session=None, var_list=None):
 """ Make Tensorflow optimization tensor. This method builds natural gradients optimization tensor and initializes all necessary variables created by the optimizer. :param model: GPflow model. :param session: Tensorflow session. :param var_list: List of tuples of variational parameters. :return: Tensorflow natural gradient operation. """

        session = model.enquire_session(session)
        with session.as_default(), tf.name_scope(self.name):
            # Create optimizer variables before initialization.
            return self._build_natgrad_step_ops(model, *var_list)