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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 get_proficiencies(self):
 """Gets the proficiency list resulting from a search. return: (osid.learning.ProficiencyList) - the proficiency list raise: IllegalState - list already retrieved *compliance: mandatory -- This method must be implemented.* """

        if self.retrieved:
            raise errors.IllegalState('List has already been retrieved.')
        self.retrieved = True
        return objects.ProficiencyList(self._results, runtime=self._runtime)