在Python中更改列表时调用函数

Question

我只是想知道您是否可以在更改列表（将项目添加到列表）时调用函数。如果有的话，它看起来像这样：

def listchanged():
    print("The list has been changed!")

list = ["apples","bananas"]
listevent(list,listchanged)

然后在外壳程序中将一个项目添加到列表中，并显示“列表已更改！”。

谢谢！

Answer 1

list更改列表时，可以子类化打印。

这是一个例子：

class EventList(list):

    def __setitem__(self, key, value):
        super(EventList, self).__setitem__(key, value)
        print("The list has been changed!")

    def __delitem__(self, value):
        super(EventList, self).__delitem__(value)
        print("The list has been changed!")

    def __add__(self, value):
        super(EventList, self).__add__(value)
        print("The list has been changed!")

    def __iadd__(self, value):
        super(EventList, self).__iadd__(value)
        print("The list has been changed!")

    def append(self, value):
        super(EventList, self).append(value)
        print("The list has been changed!")

    def remove(self, value):
        super(EventList, self).remove(value)

l = EventList(["apples","bananas"])
l.append('test')

印刷品：

The list has been changed!

要么

只需比较列表：

old_list = ["apples","bananas"]
new_list = ["apples","bananas"]
newer_list = ["apples","bananas", "oranges"]

old_list == new_list #true
old_list == newer_list #false

==如果列表在相同的索引中具有相同的元素，而不是在ID或哈希值（在lamens中）完全相同，则这将没有子类可以进行比较。只需将旧的保存在变量中，然后在要检查时使用它即可。（请注意：这并不提供自动调用打印的方法。这只是另一种方法）