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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 dataset(self):
 """ Returns the dataset that this instance belongs to. :return: the dataset or None if no dataset set :rtype: Instances """

        dataset = javabridge.call(self.jobject, "dataset", "()Lweka/core/Instances;")
        if dataset is None:
            return None
        else:
            return Instances(dataset)