A `Stack`

is a data structure that supports two basic operations: pushing a new item to the top of the stack and popping a single item from the top of the stack.

In order to implement a stack using a node class, we have to store a node that is currently referencing the top of the stack and update it during the push and pop operations.

from node import Nodeclass Stack:def __init__(self, limit=1000):self.top_item = Noneself.size = 0self.limit = limitdef push(self, value):if self.has_space():item = Node(value)item.set_next_node(self.top_item)self.top_item = itemself.size += 1else:print("All out of space!")def pop(self):if self.size > 0:item_to_remove = self.top_itemself.top_item = item_to_remove.get_next_node()self.size -= 1return item_to_remove.get_value()else:print("This stack is totally empty.")def peek(self):if self.size > 0:return self.top_item.get_value()else:print("Nothing to see here!")def has_space(self):return self.limit > self.sizedef is_empty(self):return self.size == 0

Every stack has a size that determines how many nodes it can accommodate. Attempting to push a node in a full stack will result in a stack overflow. The program may crash due to a stack overflow.

A stack is illustrated in the given image. `stackA.push(xg)`

will result in a stack overflow since the stack is already full.

A *stack* is a data structure that follows a last in, first out (LIFO) protocol. The latest node added to a stack is the node which is eligible to be removed first. If three nodes (`a`

, `b`

and, `c`

) are added to a stack in this exact same order, the node `c`

must be removed first. The only way to remove or return the value of the node `a`

is by removing the nodes `c`

and `b`

.

The stack data structure has three main methods: `push()`

, `pop()`

and `peek()`

.
The `push()`

method adds a node to the top of the stack.
The `pop()`

method removes a node from the top of the stack.
The `peek()`

method returns the value of the top node without removing it from the stack.