Stack.py

class StackNode:
 
    # Constructor to initialize a node
    def __init__(self, data):
        self.data = data 
        self.next = None
 
class Stack:
     
    # Constructor to initialize the root of linked list
    def __init__(self):
        self.root = None
 
    def isEmpty(self):
        return True if self.root is None else  False
 
    def push(self, data):
        newNode = StackNode(data)
        newNode.next = self.root 
        self.root = newNode
        print "%d pushed to stack" %(data)
     
    def pop(self):
        if (self.isEmpty()):
            return float("-inf")
        temp = self.root 
        self.root = self.root.next
        popped = temp.data
        return popped
     
    def peek(self):
        if self.isEmpty():
            return float("-inf")
        return self.root.data
 
# Driver program to test above class 
stack = Stack()
stack.push(10)        
stack.push(20)
stack.push(30)
 
print "%d popped from stack" %(stack.pop())
print "Top element is %d " %(stack.peek())