I am trying to print the program so it will look like this.

Inserting 1
Inserting 2
Inserting 3
Top element is 3
Removing 3
Removing 2
Removing 1
The stack is empty

But when I run the program, I missed "Inserting 1". My code look like this

class Node:
    def __init__(self,data):
        self.data = data
        self.next = None
    
class Stack:
    def __init__(self):
        self.head = None

    def isempty(self):
        if self.head == None:
            return True
        else:
            return False

    def push(self,data):
        if self.head == None:
            self.head=Node(data)
        else:
            newnode = Node(data)
            newnode.next = self.head
            self.head = newnode
            print("Inserting ", str(self.head.data))
    
    def pop(self):
        if self.isempty():
            return None
        else:
            poppednode = self.head
            self.head = self.head.next
            poppednode.next = None
            print("Removing",poppednode.data)
            return poppednode.data

    def peek(self):
        if self.isempty():
            return None
        else:
            return self.head.data

    def display(self):
        iternode = self.head
        if self.isempty():
            print("The stack is empty")
        else:
            while(iternode != None):
                print(iternode.data,"->",end = "")
                iternode = iternode.next
            return
        
stack = Stack()
stack.push(1)
stack.push(2)
stack.push(3)

print("Top element is ",stack.peek())

stack.pop()
stack.pop()
stack.pop()
stack.display()

CodePudding user response：

First time you push an item, self.head is None so the first block of code is executed. Unindent the print('Insert') line so it prints for both cases.

    def push(self,data):
        if self.head == None:
            self.head = Node(data)
        else:
            newnode = Node(data)
            newnode.next = self.head
            self.head = newnode
        print("Inserting ", str(self.head.data)) # <== unindent 1-level

CodePudding user response：

When you are pushing the first time self.head will be None and it won't go in the else condition where it is printing "Inserting 1"