def test_str_with_iter(self):

        class IterString(str):
            def __iter__(self):
                return iter(self + '')

        assert list(util.flatten_iterator([IterString('asdf'),
                    [IterString('x'), IterString('y')]])) == ['asdf',
                'x', 'y']
ensure that a str object with an __iter__ method (like in
dataset/ETHPy150Open zzzeek/sqlalchemy/test/base/test_utils.py/FlattenIteratorTest.test_str_with_iter