Re: extending PersistentList

On Fri, May 6, 2016 at 4:21 PM, Lars van Gemerden <[email protected]> wrote:
> Hi,
>
> I have been looking for a way to extend PersistentList in an elegant way.

Define elegant?  What are you trying to accomplish?

> I
> tried overriding the abstract methods in MutableSequence but ofcourds that
> does not work, because UserList overrides all methods in MutableSequence
> (don't know why; speed reasons?).
>
> I also tried this:
>
> class ServerFieldList(PersistentList):
>
>     def __init__(self, items, owner=None):
>         super(ServerFieldList, self).__init__(items)
>         self.owner = owner
>
>     def _get_changed(self):
>         return Persistent._get_changed(self)
>
>     def _set_changed(self, value):
>         Persistent._set_changed(self, value)
>         self.owner.__dirty__ = True
>
>     def _del_changed(self):
>         Persistent._del_changed(self)
>         self.owner.__dirty__ = True
>
>     _p_changed = property(_get_changed, _set_changed, _del_changed)
>
>
>
> but directly both calling the _get_changed etc methods in Persistent or
> using super(ServerFieldList, self) gives me an AttributeError, while i can
> clearly see these methods in Persistent. must have something to do with the
> @implementer decorator.

I guess you're looking at persistence.py.  That is only used when the
C implementation isn't used.  _get_changed etc are also internal
implementation details of the Python implementation.

 If all you want is an owner attribute a) you don't need a subclass,
and b) If you want to create a subclass to add an owner attribute,
your __init__ is more than sufficient.

You're either over thinking this, or there are some requirement you
aren't stating.

Jim

-- 
Jim Fulton
http://jimfulton.info

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