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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 crossvalidate_model(self, classifier, data, num_folds, rnd, output=None):
 """ Crossvalidates the model using the specified data, number of folds and random number generator wrapper. :param classifier: the classifier to cross-validate :type classifier: Classifier :param data: the data to evaluate on :type data: Instances :param num_folds: the number of folds :type num_folds: int :param rnd: the random number generator to use :type rnd: Random :param output: the output generator to use :type output: PredictionOutput """

        if output is None:
            generator = []
        else:
            generator = [output.jobject]
        javabridge.call(
            self.jobject, "crossValidateModel",
            "(Lweka/classifiers/Classifier;Lweka/core/Instances;ILjava/util/Random;[Ljava/lang/Object;)V",
            classifier.jobject, data.jobject, num_folds, rnd.jobject, generator)