Python成语链(flatten)无限可迭代的有限迭代？

def flatten(lst):
    """
    flatten takes a nested list and returns a flattened list

    """
    for item in lst:
        try:
            if isinstance(item, list):
                for inner_item in flatten(item):
                    yield inner_item
            else:
                yield item
        except TypeError:
            yield item

nested_list = [1, 2, ["three", 4], [5, 6, 7], ["eight", 9],
                 [10, 11]]

# Convert the list to a string so we can print the output
flattened_list_string = ', '.join(flatten(nested_list))

print(flattened_list_string)