Append item to every list in list of list

Question

I am looking to append item to every list in a list of list.

I had expected the following code to work:

start_list = [["a", "b"], ["c", "d"]]

end_list = [item.append("test") for item in start_list]

with expected output [["a", "b", "test"], ["c", "d", "test"]]

instead i get [None, None]

First, why does this occur, and second, how do i achieve the desired output?

Answer 1

append modifies the list and returns None.

If you want to generate a new list:

end_list = [item + ["test"] for item in start_list]

If you want to modify the old list:

for sublist in start_list:
    sublist.append("test")