Extend method of Python list

Question

Why does this

list(('a', 'b', 'c')).extend([1, 2, 3])

evaluate to 'None'. What I mean is that the result of a constructor should be a list, so there should be no problem "extending" it, just like if I would've assigned the result of the constructor to a variable and then extended, still the result is almost always a None. So why does this happen.

@vaultah Please close the question, if you have the privileges. — Apurva Kunkulol, Jul 20 '17 at 14:31
I can't, since I edited the tags. There should be a button saying "That solved my problem", you should click it — vaultah, Jul 20 '17 at 14:35

score -1 · Answer 1 · answered Jul 20 '17 at 14:33

-1

L = list(('a', 'b', 'c')) will create a list and assign it to the variable L. Similarly, list(('a', 'b', 'c')) will create a new list.

L.extend([1,2,3]) will perform an operation on L, with a return value of None.

So what's happening in your case is that the constructor creates a list, on which you call extend. Since extend has a return value of None, list(('a', 'b', 'c')).extend([1, 2, 3]) evaluates to None. Since the list you constructed (namely list(('a', 'b', 'c'))) wasn't assigned to a variable, there are no references to it, and python's refcounting garbage collector just sweeps up that list after the call to extend, which returns None

answered Jul 20 '17 at 14:33

inspectorG4dget

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Why did you choose to answer this question? It's obviously a duplicate, and you could close it as such with your dupe hammer. – vaultah Jul 20 '17 at 14:36
@vaultah: didn't see the dup target before I answered. Was just trying to be helpful – inspectorG4dget Jul 20 '17 at 14:47

Extend method of Python list

1 Answers1