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From: =?UTF-8?Q?Nagy_L=c3=a1szl=c3=b3_Zsolt?= <gandalf@shopzeus.com>
Newsgroups: comp.lang.python
Subject: Re: UserList - which methods needs to be overriden?
Date: Thu, 9 Jun 2016 15:33:32 +0200
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> Using the built-in list or dict is problematic because sometimes the=20
> subclass methods are ignored when the internal data is accessed (sorry,=
 I=20
> don't have an example).
Are you suggesting that I should use UserList and UserDict instead of
list and dict? What is the truth? Was UserDict left in collections for
backward compatibility, or not?

>
> How detailed is your change notification? If it's always the same metho=
d=20
> invocation you may be able to create wrappers like
>
> def whatever(self, *args):
>     try:
>         return super().whatever(*args)
>     finally:
>         self.changed()
>
> automatically, and the base class, be it list or UserList or whatever=20
> becomes a detail that can be chosen on a case by case basis.
My actual solution looks like this:


class ObservableCollection(Observable):
    @contextmanager
    def notify(self):
        self.notify_observers(EVT_BEFORE_COLLECTION_CHANGED)
        yield
        self.notify_observers(EVT_AFTER_COLLECTION_CHANGED)

class ObservableList(ObservableCollection, list):
    __slots__ =3D []

    def remove(self, value):
        with self.notify(): super().remove(value)

    def clear(self):
        with self.notify(): super().clear()

    def pop(self):
        with self.notify(): return super().pop()

It seems to be working with the built in list, dict and set types.

There must be a better way! Something like this:

@wrap_notify('remove', 'clear', 'append', 'insert', 'sort'):
class ObservableList(ObservableCollection, list):
    pass

I just can't find out the right syntax.