text: # coding:utf-8
  
  
  """自定义栈"""
  
  
  
  class Stack(object):
  
      def __init__(self):
          self.data = []
  
      def __len__(self):
          return len(self.data)
  
      def is_empty(self):
          return len(self.data) == 0
  
      def push(self, item):
          self.data.append(item)
  
      def get_top(self):
          if self.is_empty():
              return None
          return self.data[-1]
  
      def pop(self):
          if self.is_empty():
              return None
          return self.data.pop()
  
  
  
  
  
  
  
  
  
  
  