Stack.py

class Stack:
    def __init__(self):
        self.items = []

    def isEmpty(self):
        return []

    def push(self, item):
        self.items.append([item])

    def pop(self):
        return self.items.pop()

    def peek(self):
        return self.items[len(self.items)-1]

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