[Bf-python] Getters and setters in object selection

[Toni Alatalo]

I was thinking the same: as selection is not object data, maybe expose
the selection data.

Apparently that would be via the layer in Blender's case.

Was wondering whether it would make sense to have a Python selection
module, with things like:
selection.active_object
selection.selected #list of all
etc.

But I suppose better via Layer to match the actual C internals.

There is of course the concern that because the selection info used to
be accessible via object it could be confusing for folks who know the
old API.

In Unity Editor there is a Selection module which has the info like that:
https://docs.unity3d.com/ScriptReference/Selection.html

-Toni
On Mon, Nov 12, 2018 at 5:16 AM Campbell Barton <ideasman42 at gmail.com> wrote:
>
> Object.select is not really correct, since the selection state isn't
> stored in the object.
>
> If we match Blender's internal state selection would look like this:
>
> ----
> ob_base = view_layer.base_find(ob)
> if ob_base is not None:
>     ob_base.select = select
> ----
>
> In practice this is inconvenient, although I think hiding this
> relationship entirely is also a problem.
>
> In recent 2.8 builds you can optionally pass in a view layer which
> overrides the current active view layer, eg:
>
>     ob.select_set(True, view_layer)
>
> On Tue, Nov 6, 2018 at 7:02 AM Benjamin Humpherys
> <benjamin.humpherys at gmail.com> wrote:
> >
> > It makes sense that selection and visibility are not Object properties, but that’s an implementation detail that I don’t believe should to be visible in the Python API. What I’m asking is that the appropriate getter and setter functions be called through the standard python property access methods. I’m not an expert on the Python C API, but shouldn’t it be possible to use `PyGetSetDef` to redirect property access to call the new getter and setter methods, without having to expose this change to Python code? For example: https://llllllllll.github.io/c-extension-tutorial/member-vs-getset.html
> >
> > On Nov 5, 2018, at 12:15 PM, Bastien Montagne <montagne29 at wanadoo.fr> wrote:
> >
> > Hi Benjamin,
> >
> > TL;DR: We did that in 2.7x, it’s not possible anymore in 2.8x (not without **huge** changes in a large part of RNA, and adding significant complication to the API).
> >
> > Technical explanation:
> >
> > This decision was taken because selection status **is not an Object data**, not at all. It is stored in the object 'instantiation' data (called Base, and not exposed to Python) used to 'link' an object to a ViewLayer. Hence it is context-dependent info, which cannot be retrieved through our RNA property system.
> >
> > Ideally, there should be no access at all to that status in RNA, at least no setter, it should be something let to operators, or alternatively, we’d have to expose the whole Base concept to python. But that would add some noise and confusion to something already rather complicated (whole viewlayer/collection/object system).
> >
> > We have other similar accessors in Object API, like `visible_get()`, which follow the same principle (and do not have any setter).
> >
> > Note that pure-python things like @property are totally irrelevant here, this is using the semi-auto-generated binding to C code/data (through RNA), which has its own rules and limitations on top of python C API.
> >
> > Bastien
> >
> >
> > On 05/11/2018 18:37, Benjamin Humpherys wrote:
> >
> > I saw on the recent changes page on the wiki that the object selection API (https://wiki.blender.org/wiki/Reference/Release_Notes/2.80/Python_API/Scene_and_Object_API#Object_Selection_and_Hiding) has changed from a simple `obj.select` property to `select_get()` and `select_set(’SELECT’)`. I strongly urge this decision to be reconsidered because it is not idiomatic Python to use getter and setter functions, let alone setting a boolean property with a string argument!
> >
> > Instead of getters and setters please consider making `select` a @property, or utilizing `PyGetSetDef`(https://docs.python.org/3/c-api/structures.html#c.PyGetSetDef) to hide any new getter/setter logic instead of putting it in the user-facing API.
> >
> >
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>
> --
> - Campbell
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