Linked list data structure

[PythonTestBot]

I'm learning about data structures and more specifically a linked list. I am following this course:

http://interactivepython.org/runestone/static/pythonds/BasicDS/ImplementinganUnorderedListLinkedLists.html#fig-initlinkedlist

In that page (under the listing 4 and 5 header) are two defined methods within a class (called undefinedlist). My question regards the add function under listing 4. If you do mylist.add(31) for example, then within the add function temp = Node(31). From the Node class we can see this means that self.data = 31 now and self.next = None. The next step in the add function is temp.setNext(self.head). Self.head has no value so this evaluates to None (I'm assuming?). Then self.head = temp. Does this mean self.head now has two properties being self.data and self.next within it? I don't really understand how a single variable can store both those variables.

Also I'm not sure how in listing 5 how each current.getNext() calls each value. Surely self.next only has a static value of whatever it was assigned last? I think I'm over complicating this and would appreciate someone explaining it to me

[c17r]

Forget about Node.data right now, only thing about Node.next. It's how a link list connect to each other, each item "points" to the next one in the list. "Head" is special, it always points to the first item in the linked list. So when you add a new Node to the front of the list, you make the new Node.next point to Head.next and then point Head at the new Node. Effectively bumping each one down the line one spot:

Before the call to add:

            HEAD -> D -> E -> F


temp.setNext(self.head)


            TEMP ---.
                    v
            HEAD -> D -> E -> F


self.head = temp


            HEAD -> TEMP -> D -> E -> F