Report changes to an item in a collection

I'm not sure if this will be difficult, but I don't think so.

```
class Foo(object): |
def __init__(self, age): | age = 23 | age = 12
self.age = age | self.age = 23 | self.age = 12
|
def __repr__(self): |
return 'Foo({!r})'.format(self.age) |
|
def birthday(self): | |
self.age += 1 | self.age = 24 | self.age = 13
|
f = Foo(23) | f = Foo(23)
f.birthday() | f = Foo(24)
|
l = [f, Foo(12)] | l = [Foo(24), Foo(12)]
l[1].birthday() |
m = l | m = [Foo(24), Foo(13)]
```

It would be nice if the second-to-last line weren't blank. Preferably this:

```
l[1] = Foo(13)
```

This would also work:

```
l = [Foo(24), Foo(13)]
```