"add" method for linked list on python

I'm trying to write an add method for linked list on python, but it's not behaving as expected.

class linkedlist:
    def __init__(self):
       self.item=None
       self.next=None
    def add(self,val):
       self.next=self
       self.item=val

This doesn't work. When I create an object:

myobj=linkedlist()
myobj.add(1)
myobj.add(2)
print(myobj.next.item)

gives 2, instead of 1 as I would expect. Where did I go wrong?

I tried to look at Is it safe to replace a self object by another object of the same type in a method? but it's not helping.

You only have 1 object and 2 references pointing to it. You need to copy the list before adding to it:

from copy import copy

class linkedlist:
    def __init__(self):
       self.item=None
       self.next=None
    def add(self,val):
       self.next=copy(self)
       self.item=val

myobj=linkedlist()
myobj.add(1)
myobj.add(2)
print(myobj.next.item) # prints 1

To clarify:

print(myobj.item, id(myobj))
print(myobj.next.item, id(myobj.next))

with your code:

2 140520931226768
2 140520931226768 # same object!

With mine:

2 140520931224368
1 140519593761456

UPDATE:

First your expectations are wrong, you should get 3 and 2, which are the values left in the list after you popped the head. To get these results you need to update what a points to. You could do this by adding return self at the end of add and pop methods, and the reassign a:

from copy import copy

class linkedlist:
    def __init__(self):
       self.item=None
       self.next=None
    def add(self,val):
       self.next=copy(self)
       self.item=val
       return self
    def pop(self):
       self=copy(self.next)
       return self
    
a=linkedlist()
a = a.add(1)
a = a.add(2)
a = a.add(3)
a = a.add(4)
a = a.pop()
print(a.item)
a = a.pop()
print(a.item)

But IMO this is rather ugly and I would rather use Allan's approach...