Why does directly calling an index with pop work but with no arguments return none?

Question

I am rotating a simple list with lst.append(lst.pop(0))

Lst is just a populated list with [0,1,2,3. . .9]

Why does lst.append(lst.pop()) not work?
https://code.sololearn.com/clfFBUGFk691/?ref=app

Answer 1

ren if you mean why the list doesn't change, it's because pop() with no arguments returns the last value.

So what you're doing is:

1. Removing the last value of the list, which is 9
2. Adding the last value to the end of lst, which is also 9

So the result, nothing wil change.

Answer 2

But this:
print(a.append(a.pop()))

Prints None because the append method is not supposed to return any value.

Answer 3

ren that's weird, can you show us your code ? Write it in code playground, so we can test it there.

Answer 4

ren no problem 😁👍👌

Answer 5

What? For me this worked:
lst = list(range(10))
lst.append(lst.pop())

#lst equals list(range(10)) like it's supposed to.

Answer 6

I got it now I think :) thumbs up to all the helpers!!

Answer 7

Yes I had either one of these two effects- either I'd get NONE or the list remains unchanged.

Answer 8

Apologies I thought I inserted code

Answer 9

It seems that I didnt fully understand what happens with pop without arguments

Answer 10

ren If you call pop method without arguments it will use default value of -1 (index of last item).

You can find this information using help function:
help(list.pop), you'll get:

pop(self, index=-1, /)
Remove and return item at index (default last).

Raises IndexError if list is empty or index is out of range.

where -1 refers to the default value of index.

Answer 11

The append method is of class Nonetype so it returns None