链表.py

# class _Node:
#     """一个单向链表的轻量级_Node类"""
#     __slots__ = '_element','_next'
#
#     def __init__(self,element,next):
#         self._element = element
#         self._next = next

class LinkedStack:
    """单向链表实现栈"""
    #---------nested _Node class--------
    class _Node:
        """一个单向链表的轻量级_Node类"""
        __slots__ = '_element', '_next'

        def __init__(self, element, next):
            self._element = element
            self._next = next

    #-----------stack methods------------
    def __init__(self):
        self._head = None
        self._size = 0

    def __len__(self):
        return self._size

    def is_empty(self):
        return self._size == 0

    def push(self,e):
        self._head = self._Node(e,self._head)
        self._size += 1

    def top(self):
        if self.is_empty():
            raise Empty('Stack is empty')
        return self._head._element

    def pop(self):
        if self.is_empty():
            raise Empty('Stack is empty')
        answer = self._head._element
        self._head = self._head._next
        self._size -= 1
        return answer