["python","iterator","python-itertools"]
What is the difference between chain and chain.from_iterable in itertools?

I could not find any valid example on the internet where I can see the difference between them and why to choose one over the other.
The first takes 0 or more arguments, each an iterable, the second one takes one argument which is expected to produce the iterables: from itertools import chain chain(list1, list2, list3) iterables = [list1, list2, list3] chain.from_iterable(iterables) but iterables can be any iterator that yields the iterables: def gen_iterables(): for i in range(10): yield range(i) itertools.chain.from_iterable(gen_iterables()) Using the second form is usually a case of convenience, but because it loops over the input iterables lazily, it is also the only way you can chain an infinite number of finite iterators: def gen_iterables(): while True: for i in range(5, 10): yield range(i) chain.from_iterable(gen_iterables()) The above example will give you a iterable that yields a cyclic pattern of numbers that will never stop, but will never consume more memory than what a single range() call requires.