python - .extend() method returning 'None' and not the desired combination of lists I intended it to return

Question

I am playing around with some basic python methods. Right now I am experimenting with the .extend() method. I basically have two lists and want to combine them into one larger list for demonstration purposes. This works successfully (successfully as in returning the extended list) in the Shell environment, but not when saving the program. When I want to save the program and run it, it returns the value of 'None'. Any assistance would be greatly appreciated. Thank you.

listOne=[1,2,3]

listTwo=[4,5,6]

listOneandlistTwo=listOne.extend(listTwo)

print(listOneandlistTwo)

Answer 1

listOneandlistTwo=listOne.extend(listTwo)

extend() extends the given list but returns None*, so you have extended listOne with the contents of listTwo and assigned None to listOneandListTwo.

What you want (assuming you want to leave listOne and listTwo as they are) is this:

listOneandlistTwo = listOne + listTwo

* This behavior is by design. If extend() returned the extended list, would it return a copy that's extended? Or would it return the original list extended? It's another detail to remember, so by returning None you are meant to think, "oh, since it's returning None it must be extending the list in place, otherwise it'd be useless."