[Bf-python] Addon's can no longer access context on activation.

[Campbell Barton]

>From what I can tell you dont even need to access the scene on load.

On Thu, Dec 20, 2012 at 12:55 PM, dimitris chloupis
<thekilon at yahoo.co.uk> wrote:
> No idea what you talking about . No idea how to access bpy.context.scene
> while the addon loads.
>
> my access to bpy.context.scene happens here ->
> https://github.com/kilon/Gyes/blob/master/gyes/random_material_generator.py#L67
Quite sure you can replace:
if hasattr(bpy.context.scene , "historybak")==False:
with...
if hasattr(bpy.types.Scene, "historybak")==False:

> and here ->
> https://github.com/kilon/Gyes/blob/master/gyes/random_material_generator.py#L622
This will continue to work without problems.

>
> in first case I check whether there is a historybak prop in scene , so there
> is no assumptions here
> and blender has no reason to crash. Because I check if it exists in the
> first place.
> If the prop does not exists it gets created in the process.
>
> in second case the history is restored when the user clicks the button.
>
> In any cases there is no chance that the addon would access non existant
> properties
> because I like to leave nothing to chance ;)
>
> unless you try to tell me something else here that I dont understand
> or I missed a possible scenario . I am all ears :)
>
> ________________________________
> From: Campbell Barton <ideasman42 at gmail.com>
> To: dimitris chloupis <thekilon at yahoo.co.uk>; Blender Foundation Python list
> <bf-python at blender.org>
> Sent: Thursday, 20 December 2012, 14:33
> Subject: Re: [Bf-python] Addon's can no longer access context on activation.
>
> On Thu, Dec 20, 2012 at 12:09 PM, dimitris chloupis
> <thekilon at yahoo.co.uk> wrote:
>> I am the developer of Gyes ( random material and texture generator). The
>> reason why Gyes
>> use bpy.context.scene is to store a property that store presets of
>> randomised materials / textures.
>> I wanted the data to be stored/saved with the blend file and be associated
>> with the scene curently loaded
>> as global scene presets and not specific presets to objects or any other
>> 3d
>> asset.
>>
>> I am not sure if removing bpy.context.scene is a good idea in the first
>> place, unless there is another way to save
>> , store scene presets together with the blend file. If so , then gladly I
>> will update my addon. But if not , it basically
>> cripples / makes useless my history tool ->
>>
>> http://wiki.blender.org/index.php/Extensions:2.6/Py/Scripts/System/Gyes/History-Tool
>>
>>
>> ________________________________
>> From: Campbell Barton <ideasman42 at gmail.com>
>> To: Blender Foundation Python list <bf-python at blender.org>; bf-blender
>> developers <bf-committers at blender.org>
>> Sent: Thursday, 20 December 2012, 4:38
>> Subject: [Bf-python] Addon's can no longer access context on activation.
>>
>> Recently I've noticed addons using bpy.context.scene when being
>> imported or in the register() function.
>>
>> This is really bad practice and will cause inconsistency if the addon
>> is enabled and a different blend file is loaded.
>> In the worst case accessing a removed datablock can crash which is
>> likely if a datablock is stored as a global variable on activation -
>> object_laplace_lightning.py does this.
>>
>> I've changed addon loading so that they only get access to a
>> restricted context which only exposes 'window_manager' - needed for
>> adding keymaps.
>>
>>
>> Accessing other attributes now errors out with...
>>
>>  AttributeError: '_RestrictedContext' object has no attribute 'scene'
>>
>> The addons distributed with blender don't do this but some contrib
>> addons do, so they will need updating
>> (release/scripts/addons_contrib).
>>
>> ----
>>    add_mesh_clusters
>>    gyes
>>    io_atomblend_utilities
>>    io_export_marmalade
>>    io_import_LRO_Lola_MGS_Mola_img
>>    io_import_lipSync_Importer
>>    mesh_edgetools
>>    mesh_fiber
>>    mesh_show_vgroup_weights
>>    node_categories
>>    object_laplace_lightning
>>    online_mat_lib
>>    sequencer_extra_actions
>>    space_view3d_quickPrefs
>>
>> If any devs want some help updating their addons you can ask on
>> bf-python mailing list, though in all cases I've seen its quite
>> straightforward.
>>
>> --
>> - Campbell
>
> Access has only been removed on loading the addon.
>
> The solution is just not to access presets when the addon loads and
> register()'s,
> during execution you still have regular access to the context
> (operators, panels etc).
>
> Since the scene at load time may very well not be the same scene when
> the script executes (if the user loads a new file), whatever changes
> made at load time are likely lost.
>
> --
> - Campbell
>
>
>
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-- 
- Campbell