def largest_key(self):
        '''D.largest_key() -> the largest key; raise KeyError if D is empty.'''
        try:
            return self._sorted_keys[-1]
        except IndexError:
            raise KeyError('largest_key(): dictionary is empty')
D.largest_key() -> the largest key; raise KeyError if D is empty.
recipes/Python/576998_Sorted_dictionary/recipe-576998.py