Stack Implementation.py

#Python program for implementation of stack using linked list
#Class to represent node
class Node:
    #constructor to intialize node
    def __init__(self,data):
        self.data=data
        self.next=None

class Stack:
    #Constructor to intialize root of linked list
    def __init__(self,root):
        self.root=None
    def isempty(self):
        return True if self.root is None else False
    def push(data):
        newnode=Node(data)
        newnode.next=root
        root=newnode
    def pop():
        if isempty():
            return 0
        temp=root
        root=root.next
        popped=temp.data
        return popped
    def peek():
        if isempty():
            return 0
        return root.data
#program to test above function
    stack=stack()
    stack.push(5)
    stack.push(10)
    stack.push(15)
     print stack.pop
     print stack.peek



#implementing stack using arrays
#import maxsize from sys.Maxsize returns infinite when stack is empty.
from sys import maxsize
#function to create a stack.initial size of stack is zero
def createstack():
    stack=[]
    return stack
if isempty(stack):
    return len(stack)==0
    
#push function to add an item on the stack.Increases stack size by 1
def push(stack,item):
    stack.append(item)
    print ("item pushed"+item)
#pop function to remove item from stack.Decreases stack size by 1.
def pop(stack):
    if (isempty(stack)):
        return str(-maxsize-1)
    stack.pop()
#peek function.return top element of the stack
def peek(stack):
    if (isempty(stack)):
        return str(-maxsize-1)
    return stack[-len(stack)-1]
#driver program to test the above functions
stack=createstack()
push(stack,str(10))
push(stack,str(20))
push(stack,str(30))
push(stack,str(40))
print(pop(stack) +" is popped from stack")
print("top item is "+peek(stack))