text: class ListStack:
      def __init__(self):
          self._L = []
  
      def push(self, item):
          self._L.append(item)
  
      def pop(self):
          return self._L.pop()
  
      def peek(self):
          return self._L[-1]
  
      def __len__(self):
          return len(self._L)
  
      def isempty(self):
          return len(self) == 0
  
  
  