Python - Extending a list directly results in None, why?

Question

x=[1,2,3]
x.extend(\'a\')

Output:

x is [1,2,3,\'a\']

But when I do the following:

[1,2,3].extend(\'a\         


        

Answer 1

list.extend modifies the list in place and returns nothing, thus resulting in None. In the second case, it's a temporary list that is being extended which disappears immediately after that line, while in the first case it can be referenced via x.

to append a listB to a listA while trying to extend listC to listB.

Instead of using extend, you might want to try this:

listA.append(listB[15:18] + listC[3:12])

Or do it in multiple simple lines with extend if you want to actually modify listB or listC.

Answer 2

extend will extend list it self. Return type of that method is None

If you want to union 2 list and add that list to another list then you have to use another way to add.

listB[15:18] = listC[3:12]
listA.extend(listB)