栈

class Stack():
    def __init__(self):
        self.stack = []
    def push(self,value):
        self.stack.append(value) #进栈
    def pop(self):
        if self.stack:
            self.stack.pop() #出栈
        else:
            raise LookupError('stacke is empty')
    def is_empty(self):
        return bool(self.stack) 
    def top(selfs):
       return selfs.stack[-1]
    def size(self):
        return len(self.stack)   

stack = Stack()
stack.push(5)
print(stack.top())
stack.push(6)
print(stack.size())
stack.pop()
stack.pop()
print(stack.is_empty())