stack.py

class Stack:
    def __init__(self):
        self.values = list()

    def push(self, element):
        self.values.append(element)

    def isEmpty(self):
        return len(self.values) == 0

    def pop(self):
        if not (self.isEmpty()):
            return self.values.pop()
        else:
            print('Stack Underflow')
            return None

    def top(self):
        if not (self.isEmpty()):
            return self.values[-1]
        else:
            print('Stack Empty')
            return None

    def size(self):
        return len(self.values)

    def __str__(self):
        stringRepr = ''
        for i in reversed(self.values):
            stringRepr += str(i) + '\t'
        return stringRepr