python 栈 ~

class Stack:	def __init__(self):		self.items = []	def isEmpty(self):		return len(self.items)==0	def push(self,item):		self.items.append(item)	def pop(self):		return self.items.pop()	def peek(self):		if not self.isEmpty():			return self.items[len(self.items)-1]	def size(self):		return len(self.items)if __name__ == '__main__':	s=Stack()	PRint(s.isEmpty())	s.push(4)	s.push('dog')	print(s.peek())	s.push(True)	print(s.size())	print(s.isEmpty())	s.push(8.4)	print(s.pop())	print(s.pop())	print(s.size())