Hook into adding / removing items from list in python

I'd like to create a drop-in replacement for python's list, that will allow me to know when an item is added or removed. A subclass of list, or something that implements the list interface will do equally well. I'd prefer a solution where I don't have to reimplement all of list's functionality though. Is there a easy + pythonic way to do it?

Pseudocode:

class MyList(list):
    # ...
    def on_add(self, items):
        print "Added:"
        for i in items:
            print i

    # and the same for on_remove

l =开发者_如何学运维 MyList()
l += [1,2,3]
# etc.

To see what functions are defined in list, you can do

>>> dir(list)

Then you will see what you can override, try for instance this:

class MyList(list):
    def __iadd__(self, *arg, **kwargs):
        print "Adding"
        return list.__iadd__(self, *arg, **kwargs)

You probably need to do a few more of them to get all of it.

The documentation for userlist tells you to subclass list if you don't require your code to work with Python <2.2. You probably don't get around overriding at least the methods which allow to add/remove elements. Beware, this includes the slicing operators.