# adapted from
# https://runestone.academy/runestone/books/published/
# pythonds/BasicDS/ImplementingaStackinPython.html

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

     def is_empty(self):
         return self.items == []

     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 main():
    s = Stack()
    print("push(1), push(2), then pop() until empty.")
    s.push(1)
    s.push(2)
    while not s.is_empty():
        print(s.pop())

main()