concatenating sublists python [duplicate]

Question

I have one list like: n = [[1, 2, 3], [4, 5, 6, 7, 8, 9]]

I want to create a function that takes a single list (see above) and concatenates all the sublists that are part of it into a single list.

Answer 1

n = [[1, 2, 3], [4, 5, 6, 7, 8, 9]]
nn = [ x for y in n for x in y]

Answer 2

>>> lst = [[1, 2, 3], [4, 5, 6, 7, 8, 9]]
>>> from itertools import chain
>>> list(chain.from_iterable(lst))
[1, 2, 3, 4, 5, 6, 7, 8, 9]