[Bf-committers] Custom Properties - python issues

[Campbell Barton]

Hi, there are indeed some loose ends with id property & UI integration
as you have noticed. This is an area which can worked on but for the
mostpart python defined RNA is the way to go.

reply inline.

On Sat, Jan 1, 2011 at 9:41 AM, Hart's Antler <bhartsho at yahoo.com> wrote:
> 1. KeyError: 'the length of IDProperty names is limited to 31 characters'object['x'*32] = 'why not make the limit 32 or 64?, 31 is an odd number - not possible to use md5sum hashes either as a workaround'

 its annoying but with a fixed allocation size per item its not so
simple to avoid.
* Allocating the strings each would cause worse problem with small
allocations then we already have.
* Changing the fixed length higher then 31 could work but would mean
opening files in older blender versions would be incompatible.
* having a limit of 32 and ensure all string functions limit to 32
chars could work too (use strncpy rather then strcpy) could work but
also would give problems with
loading new files on older blenders. for a 1 char gain I don't think
its worth it.

This is similar to being able to having object names longer then 21 chars.
known problem and not trivial to fix.

> 2. inner single quotes are invalid## this failslayout.prop( object, "['my-custom-prop']" )              # a better warning should be printed, or single quotes should be supported## this works - double quotes must be usedlayout.prop( object, '["my-custom-prop"]' )

The issue here is that we are using the animation path lookup for the
UI as well, see: RNA_path_resolve(), since this is potentially
evaluated 100's, even 1000s of times a frame update, and not compiled
into bytecode (as with python), I prefer not to confuse this as being
a language or being python compatible. and keep path evaluation simple
where possible.

We could raise an error if "['foo']" is passed to a UI function to
avoid confusion.

> 3. dicts are allowed, but layout.prop(...) can not show each subkey on its own## (the dict can be viewed as a string from Custom Properties Panel, but thats not very useful for the user) ##object['x'] = {'a':1, 'b':2}box.prop( object, '["x"]["a"]' )               # error: rna_uiItemR: property not found: Object.["x"]["a"]box.prop( object, '["x"]' )          # this also fails

This is just not supported yet, direct ID property access isnt
compleate, best define your own RNA in most cases as Tom Edwards
pointed out.

> 4. booleans not supported by custom propertiesobject['my-custom-prop'] = True
Yes, ID properties only support ints, floats. Again, using RNA you can
define booleans.
its not that hard to add boolean support to ID properties so//
ob["mybool"] = True
...is not the same as
ob["mybool"] = 1

I don't think this is a big limitation, boolean is a subclass of an
int in python, "1 == True" works as if both are 1.

# converted to 1 without any warninglayout.prop( object,
'["my-custom-prop"]', toggle=True )    # toggle is ignored, numeric
entry is displayed instead
> ## workaround ##class mypanel(bpy.types.Panel): bl_space_type = 'PROPERTIES'    bl_region_type = 'WINDOW'       bl_context = "object"   bl_label = "toggle custom prop example" @classmethod    def poll(cls, context): return True     def draw(self, context):                layout = self.layout            ob = context.active_object              tag = 'my-custom-prop'          if tag not in ob.keys(): ob[tag] = True         v = ob[tag]             if v: icon = 'CHECKBOX_HLT'             else: icon = 'CHECKBOX_DEHLT'           op = layout.operator( 'toggle_prop', text=tag, icon=icon )              op.propname = tag
> class toggle_prop_op(bpy.types.Operator):                       '''operator: prop toggle helper'''      bl_idname = "toggle_prop"       bl_label = "toggle"                     bl_options = {'REGISTER', 'UNDO'}       propname = StringProperty(name="property name", description="...", maxlen=32, default="")       @classmethod    def poll(cls, context): return True     def invoke(self, context, event):               ob = context.active_object              ob[ self.propname ] = not ob[ self.propname ]           return {'FINISHED'}
>
>
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-- 
- Campbell