[Python] Python - Reverse Linked List Issue

I have been working on the reverse linked list method for a long time and I am trying to understand why it is wrong but I can't seem to get it. The following is my function.

def reverse(self, head):
if head is None or head.next is None:
return head

prev = None
current = head

while current is not None:
temp = current
current.next = prev
prev = temp
current = prev.next

return prev


I thought the above reverse function should work. Example SLL: 1 -> 2 -> 3 -> None
My thought process:

1. Set temp to reference to the current which is the head of the linked list. Thus, temp.val = 1 and temp.next.val = 2.
   
2. current.next = prev means that the current is now pointing to None.
   
3. prev = temp means that prev.val = 1 and prev.next.val = 2
   
4. current = prev.next means that current.val = 2 and current.next.val = 3

Is my thought process correct? If not, which step is incorrect? I also searched up the "correct" way of doing this where

while current is not None:
temp = current.next
current.next = prev
prev = current
current = temp


This works but I want to understand why my way of doing it is incorrect. I don't want to memorise blindly.

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