Stack

Introduction

A stack is a container of objects that are inserted and removed according to the last-in first-out (LIFO) principle. In the pushdown stacks only two operations are allowed: push the item into the stack, and pop the item out of the stack. A stack is a limited access data structure - elements can be added and removed from the stack only at the top. Here is a structural definition of a Stack: a stack is either empty or it consists of a top and the rest which is a Stack.

Syntax

stack = [] # Create the stack
stack.append(object) # Add object to the top of the stack
stack.pop() -> object # Return the top most object from the stack and also remove it
list[-1] -> object # Peek the top most object without removing it

Remarks

Due to the way their elements are accessed, stacks are also known as Last-In, First-Out (LIFO) stacks.

In Python one can use lists as stacks with append() as push and pop() as pop operations. Both operations run in constant time O(1).

The Python’s deque data structure can also be used as a stack. Compared to lists, deques allow push and pop operations with constant time complexity from both ends.

Found a mistake? Have a question or improvement idea? Let me know.

Table Of Contents