python - 为什么这会给出 AttributeError？（在 Python 中访问类属性）

Question

我有以下堆栈的实现：

class Stack:
    len = 0
    def __init__(self):
        self.items = []
        self.len = 0

    # isEmpty() - returns True if stack is empty and false otherwise
    def isEmpty(self):
        return self.items == []
    # push() - Insert item at the top of the stack
    def push(self,item):
        self.items.append(item)
        self.len = self.len + 1

    # pop() - Remove and return element from top of the stack,
    # provided it is not empty
    def pop(self):
        return self.items.pop()
        self.len = self.len - 1

    # also known as peek() - return top element from stack without removing,
    #
    def top(self):
        return self.items[len(self.items)-1]

当我尝试访问lenmain() 中的属性时，它会给出属性错误....

import ADT as ADT
def main():
    stack = ADT.Stack()
    print (stack)

AttributeError: 'Stack' object has no attribute 'len'

这是怎么回事？我试过 getattr() 也失败了。

标签： pythonattributesstackattributeerrorabstract-data-type