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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 _eval(self, node):
 """ Evaluate a node :param node: Node to eval :return: Result of node """

        try:
            handler = self.nodes[type(node)]
        except KeyError:
            raise ValueError("Sorry, {0} is not available in this evaluator".format(type(node).__name__))

        return handler(node)