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:
itertools.chain(list1, list2, list3) iterables = [list1, list2, list3] itertools.chain.from_iterable(iterables)
iterables can be any iterator that yields the iterables.
def generate_iterables(): for i in range(10): yield range(i) itertools.chain.from_iterable(generate_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 a infinite number of finite iterators:
def generate_iterables(): while True: for i in range(5, 10) yield range(i) itertools.chain.from_iterable(generate_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.