from typing import Optional	class ArrayStack:	def __init__(self, nums):	# 初始化数组	self._data = list()	# 数组的大小	self._nums = nums	# 数组元素个数	self._count = 0	def push(self, data) -> bool:	'''	入栈	:param data:	:return:	'''	if (self._count + 1) == self._nums:	# 栈已经满了	return False	self._data.append(data)	self._count += 1	return True	def pop(self) -> Optional[int]:	'''	出栈	:return:	'''	if self._count:	value = self._data[self._count - 1]	self._data.pop(self._count - 1)	self._count -= 1	return value	def __repr__(self) -> str:	'''	打印栈	:return:	'''	nums = reversed(self._data)	return " ".join("[{}]".format(num) for num in nums)	if __name__ == '__main__':	stack = ArrayStack(10)	for i in range(15):	stack.push(i)	# 输出：[8] [7] [6] [5] [4] [3] [2] [1] [0]	print(stack)	for _ in range(5):	stack.pop()	# 输出：[3] [2] [1] [0]	print(stack)

from typing import Optional	# 链表结点类	
class Node:	def __init__(self, data: int, next=None):	self._data = data	self._next = next	class LinkedStack:	"""	链表实现的栈	"""	def __init__(self):	self._top = None	def push(self, value: int):	'''	入栈，将新结点放在链表首部	:param value:	:return:	'''	new_top = Node(value)	new_top._next = self._top	self._top = new_top	def pop(self) -> Optional[int]:	if self._top:	value = self._top._data	self._top = self._top._next	return value	def __repr__(self) -> str:	'''	打印栈元素	:return:	'''	current = self._top	nums = []	while current:	nums.append(current._data)	current = current._next	return " ".join("[{}]".format(num) for num in nums)	if __name__ == '__main__':	stack = LinkedStack()	# 入栈	for i in range(9):	stack.push(i)	# 输出：入栈结果:  [8] [7] [6] [5] [4] [3] [2] [1] [0]	print('入栈结果: ', stack)	# 出栈	for _ in range(3):	stack.pop()	# 输出：出栈结果:  [5] [4] [3] [2] [1] [0]	print('出栈结果: ', stack)

def add(x, y):	sum = x + y	return sum	def main():	a = 1	ret = 0	res = 0	ret = add(3, 5)	res = a + ret	print('%d', res)

from Stack.linked_stack import LinkedStack	
import copy	class NewLinkedStack(LinkedStack):	def is_empty(self):	return not self._top	class Browser():	def __init__(self):	# forward_stack 保存打开浏览器或者前进时候的页面	self.forward_stack = NewLinkedStack()	# back_stack 保存后退时候从 forward_stack 弹出的页面	self.back_stack = NewLinkedStack()	def can_forward(self):	if self.back_stack.is_empty():	return False	return True	def can_back(self):	if self.forward_stack.is_empty():	return False	return True	def open(self, url):	print('Open new url {}'.format(url))	self.forward_stack.push(url)	def back(self):	if self.forward_stack.is_empty():	return	# 点击后退按钮，从 forward_stack 中弹出当前页面，并保存到 back_stack 中	top = self.forward_stack.pop()	self.back_stack.push(top)	print('back to {}'.format(top))	def forward(self):	if self.back_stack.is_empty():	return	# 点击前进按钮，从　back_stack 中弹出，然后保存到 forward_stack 中	top = self.back_stack.pop()	self.forward_stack.push(top)	print('forward to {}'.format(top))	def __repr__(self):	copy_forward_stack = copy.deepcopy(self.forward_stack)	url_list = list()	while not copy_forward_stack.is_empty():	url_list.append(copy_forward_stack.pop())	return " ".join("{}".format(url) for url in url_list)	if __name__ == '__main__':	browser = Browser()	browser.open('a')	browser.open('b')	browser.open('c')	print('open the browser: {}'.format(browser))	if browser.can_back():	browser.back()	if browser.can_forward():	browser.forward()	browser.back()	browser.back()	browser.back()	print('browser: {}'.format(browser))	

Open new url a	
Open new url b	
Open new url c	
open the browser: c b a	
back to c	
forward to c	
back to c	
back to b	
back to a	
browser: