stack.py

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

    def is_empty(self):  # 스택이 비었는가
        return len(self.items) == 0

    def push(self, item):
        self.items.append(item)  # 빈칸

    def pop(self):
        if not self.is_empty():
            return self.itemas.pop()
        else:
            return None

    def peek(self):
        if not self.is_empty():
            return self.items[-1]
        else:
            return None


stack = Stack()
stack.push(1)
stack.push(2)
stack.push(3)

print("스택 크기:", stack.size())
print("스택 최상단요소:", stack.peek())
print("스택에서 꺼낸 요소:", stack.pop())
print("스택 크기:", stack.size())
print("스택이 비었냐?:", stack.is_empty())