Python - Extending A List Directly Results In None, Why?

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') Output: None Why does extend work on a list reference, but not on a list? 2nd

Solution 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.

Solution 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)