Stack in Python

In Python, a Stack is a data structure that follows the LIFO(Last In First Out) technique to store data. Stack provides two operations to implement it.

push method:- to add an element to the top of the stack.
pop method:- to remove an element from the top of the stack.

Stack class with methods for pushing, popping, checking if the stack is empty, getting the size of the stack, and peeking at the top element.

Create Custom Stack Class:

# Declaring Custom Stack Class
class Stack:
    
    # constructor automatically invoked once, stack instance created.
    # it will items array which is associated with class instance
    def __init__(self):
        self.items = []

    # push function to add item in the end of stack.
    def push(self, item):
        self.items.append(item)

    def size(self):
        return len(self.items)

     # pop function to remove last item from stack.
    def pop(self):
        if not self.is_empty():
            return self.items.pop()
        else:
            print("Stack is empty")
            return None

    def is_empty(self):
        return len(self.items) == 0

    def peek(self):
        if not self.is_empty():
            return self.items[-1]
        else:
            print("Stack is empty")
            return None

# stack instance created
s = Stack()

Add Elements in Stack and Check Size of Stack:

Add items within the stack by calling the `push()` function of Stack Class.

Example:

# adding items within stack by calling push function of Stack Class.
s.push(1)
s.push(2)
s.push(3)

# Print the size of stack
print("Size of the stack:", s.size())  # Output: 3

Check Peek value in Stack:

Example:

# print peek value in stack else peek function will return None Data Type value
print("Stack Peek Value: ", s.peek())  # Output: 3

Checking Peek value in Stack else return None Data Type value

Remove Elements from Stack:

Example:

# pop function to remove last item from stack.
 def pop(self):
   if not self.is_empty():
     return self.items.pop()
   else:
     print("Stack is empty")
     return None

Add pop method in stack class

If no element exist in stack then it will return "Stack is empty" message

Example: remove value from stack

print("Popping elements:")

# Remove last element from stack
print(s.pop())  # Output: 3

# Remove last element from stack
print(s.pop())  # Output: 2

# Remove last element from stack
print(s.pop())  # Output: 1

# Remove last element from stack
print(s.pop())  # Output: Stack is empty, None

Note:

Create an empty stack: stack = "Stack()".
Check if the stack is empty: "stack.is_empty()".
Push an item onto the stack: "stack.push(item)".
Get the size of the stack: "stack.size()".
Check the Peek value in the stack without removing items: "stack.peek()".
Pop the top item from the stack: "stack.pop()".

<-- Queue

Decorator -->