stackmaxelem.py

class Node(object):
    def __init__(self,val=None,curMax=None):
        self.val = val
        self.curMax = curMax

    def __repr__(self):
        return str(self.data)

class Stack(object):
    def __init__(self):
        self.items = []
    def __str__(self):
        return "Size is {}".format(len(self.items))
    def push(self,data):
        self.items.append(data)
    def isEmpty(self):
        if len(self.items) ==0:
            return True
        return False
    def pop(self):
        self.items.pop()
    def top(self):
        if self.isEmpty():
            return None
        return self.items[-1]
    def delete(self):
        self.items[-1].pop()
    def max(self):
        return max(self.items)

n = int(input())
s = Stack()
maxel = 0
for i in range(n):
    c = input()
    code = c.split(" ")
    if code[0] == "1":
        code1 = int(code[1])
        maxel = max(code1,maxel)
        s.push(Node(code1,maxel))
    if code[0] == "2":
        if(not s.isEmpty()):
            s.pop()
        if s.isEmpty():
            maxel = 0
        else:
            maxel = s.top().curMax
    if code[0] == "3":
        if (not s.isEmpty()):
            print(s.top().curMax)