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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 label_values(self):
 """ Return a list of all occuring label values. Returns: list: Lexicographically sorted list (str) of label values. Example: ['a', 'b', 'c', 'd'] """


        all_labels = set([l.value for l in self])
        return sorted(all_labels)