Python Data Structures and Algorithms

Pop operation

Now we need a pop method to remove the top element from the stack. As we do so, we need to return the topmost element as well. We will make the stack return None if there are no more elements:

    def pop(self):         if self.top:             data = self.top.data             self.size -= 1              if self.top.next:                 self.top = self.top.next             else:                 self.top = None             return data         else:             return None 

The thing to pay attention to here is the inner if statement. If the top node has its next attribute pointing to another node, then we must set the top of the stack to now point to that node:

When there is only one node in the stack, the pop operation will proceed as follows: ...