def smallest_key(self):
        '''D.smallest_key() -> the smallest key; raise KeyError if D is empty.'''
        try:
            return self._sorted_keys[0]
        except IndexError:
            raise KeyError('smallest_key(): dictionary is empty')
D.smallest_key() -> the smallest key; raise KeyError if D is empty.
recipes/Python/576998_Sorted_dictionary/recipe-576998.py