API: bpy.props getter function returns KeyError instead of default value #98939

New Issue

Crowe · 2022-06-16T16:51:28+02:00

Crowe commented

2022-06-16 16:51:28 +02:00

System Information
Operating system: Windows-8.1 64 Bits
Graphics card: NVIDIA GeForce GTX 1060 6GB/PCIe/SSE2 4.5.0 NVIDIA 466.47

Blender Version
Broken: 3.2.0, branch: master, hash: e05e1e3691
Worked: Unknown

Short description of error
I'm not entirely sure whether it's a bug or an omission in the docs , but attempting to retrieve a self[prop] inside a getter function for a property that hasn't been manually set yet results in a KeyError rather than returning the default.

Sample Code:

import bpy

from bpy.types import (
    Panel,
    PropertyGroup,
)
from bpy.props import (
    IntProperty,
    PointerProperty,
)

- ------------------------------------------------------------------------
- Properties
- ------------------------------------------------------------------------
- Getter
def get_prop(self):
    print("Get me:", self.get("test", "Missing value"))

    return self["test"]
    
# Setter
def set_prop(self, value):
    print("Set me:", value)

    self["test"] = value


class CustomProperties(PropertyGroup):
    # Temporarily store data in custom props to display and edit in 3D view panel        
    @classmethod
    def register(cls):

        # OBJECT test
        bpy.types.Object.custom_props = PointerProperty(
            name="Custom Properties",
            description="Store them here!",
            type=cls,
        )

        # Property Group
        cls.test = IntProperty(
            name="Prop from Group",
            description="I should be registered in a Property Group",
            default=10,
            get=get_prop,
            set=set_prop,
        )
        
        # Direct Prop
        bpy.types.Object.test = IntProperty(
            name="Direct Prop",
            description="I should be registered directly onto an Object",
            default=20,
            get=get_prop,
            set=set_prop,
        )


    # Clear when unregistering
    @classmethod
    def unregister(cls):
        del bpy.types.Object.custom_props
        del bpy.types.Object.test


- ------------------------------------------------------------------------
- Panel
# ------------------------------------------------------------------------

# --- Hair Nodes System Properties Panel ---
class PANEL_PT_TestCustomProp(Panel):  
    bl_space_type = "VIEW_3D"
    bl_category = "Test Panel"
    bl_region_type = "UI"
    bl_label = "Display Prop Here"
    bl_idname = "VIEW3D_PT_testCustomPanels"
    
    def draw(self, context):
        layout = self.layout
        obj = context.active_object

        layout.prop(obj, "test")
        layout.prop(obj.custom_props, "test")

CLASSES = [
    CustomProperties,
    PANEL_PT_TestCustomProp,
]

def register():
    for cls in CLASSES:
        bpy.utils.register_class(cls)

def unregister():
    for cls in CLASSES:
        bpy.utils.unregister_class(cls)  

if __name__ == "__main__":
    register()

Result:

This is an issue because the docs lead the user to believe its provided example would work similarly to the default get function. That's not the case. The example won't work at all, it'll spit an error.

In case not returning the default is the intended behavior, it'd be good to clearly point this out in the docs, perhaps providing a code snippet that more closely mimics the default getter function behavior instead of the current sample code.

Example:

# Plain Getter
def group_prop(self):
    print("Get me:", self.get("test", "Missing value"))

    if (value := self.get("test")) == None:
        print("Not found. Retrieving default.")
        value = bpy.context.active_object.bl_rna.properties["test"].default

        - Alternatively you can set the value then return self["test"] as usual
        - self["test"] = value

    return value

# Getter for a prop in a PropertyGroup
def get_group_prop(self):
    print("Get me:", self.get("test", "Missing value"))

    if (value := self.get("test")) == None:
        print("Not found. Retrieving default.")
        value = bpy.context.active_object.custom_props.bl_rna.properties["test"].default

    return value

Exact steps for others to reproduce the error

Use the sample code provided to register the test properties and a new panel to display them.
Take a look at the System Console or attempt to output the prop values in the Python Console.
Manually set the properties. The getter function "get_prop" works now.

**System Information** Operating system: Windows-8.1 64 Bits Graphics card: NVIDIA GeForce GTX 1060 6GB/PCIe/SSE2 4.5.0 NVIDIA 466.47 **Blender Version** Broken: 3.2.0, branch: master, hash: e05e1e369187 Worked: Unknown **Short description of error** I'm not entirely sure whether it's a bug or an omission in the [docs ](https://docs.blender.org/api/current/bpy.props.html#getter-setter-example), but attempting to retrieve a `self[prop]` inside a **getter function** for a property that hasn't been manually set yet results in a KeyError rather than returning the default. Sample Code: ``` import bpy from bpy.types import ( Panel, PropertyGroup, ) from bpy.props import ( IntProperty, PointerProperty, ) - ------------------------------------------------------------------------ - Properties - ------------------------------------------------------------------------ - Getter def get_prop(self): print("Get me:", self.get("test", "Missing value")) return self["test"] # Setter def set_prop(self, value): print("Set me:", value) self["test"] = value class CustomProperties(PropertyGroup): # Temporarily store data in custom props to display and edit in 3D view panel @classmethod def register(cls): # OBJECT test bpy.types.Object.custom_props = PointerProperty( name="Custom Properties", description="Store them here!", type=cls, ) # Property Group cls.test = IntProperty( name="Prop from Group", description="I should be registered in a Property Group", default=10, get=get_prop, set=set_prop, ) # Direct Prop bpy.types.Object.test = IntProperty( name="Direct Prop", description="I should be registered directly onto an Object", default=20, get=get_prop, set=set_prop, ) # Clear when unregistering @classmethod def unregister(cls): del bpy.types.Object.custom_props del bpy.types.Object.test - ------------------------------------------------------------------------ - Panel # ------------------------------------------------------------------------ # --- Hair Nodes System Properties Panel --- class PANEL_PT_TestCustomProp(Panel): bl_space_type = "VIEW_3D" bl_category = "Test Panel" bl_region_type = "UI" bl_label = "Display Prop Here" bl_idname = "VIEW3D_PT_testCustomPanels" def draw(self, context): layout = self.layout obj = context.active_object layout.prop(obj, "test") layout.prop(obj.custom_props, "test") CLASSES = [ CustomProperties, PANEL_PT_TestCustomProp, ] def register(): for cls in CLASSES: bpy.utils.register_class(cls) def unregister(): for cls in CLASSES: bpy.utils.unregister_class(cls) if __name__ == "__main__": register() ``` Result: ![blender_prop_getter_missing_default.jpg](https://archive.blender.org/developer/F13174410/blender_prop_getter_missing_default.jpg) This is an issue because the docs lead the user to believe its provided example would work similarly to the default get function. That's not the case. The example won't work at all, it'll spit an error. In case not returning the default is the intended behavior, it'd be good to clearly point this out in the docs, perhaps providing a code snippet that more closely mimics the default getter function behavior instead of the current sample code. Example: ``` # Plain Getter def group_prop(self): print("Get me:", self.get("test", "Missing value")) if (value := self.get("test")) == None: print("Not found. Retrieving default.") value = bpy.context.active_object.bl_rna.properties["test"].default - Alternatively you can set the value then return self["test"] as usual - self["test"] = value return value # Getter for a prop in a PropertyGroup def get_group_prop(self): print("Get me:", self.get("test", "Missing value")) if (value := self.get("test")) == None: print("Not found. Retrieving default.") value = bpy.context.active_object.custom_props.bl_rna.properties["test"].default return value ``` **Exact steps for others to reproduce the error** 1. Use the sample code provided to register the test properties and a new panel to display them. 2. Take a look at the System Console or attempt to output the prop values in the Python Console. 3. Manually set the properties. The getter function "get_prop" works now.

Crowe commented

2022-06-16 16:51:28 +02:00

Added subscriber: @crowe

Pratik Borhade commented

2022-06-17 06:11:02 +02:00

Added subscriber: @PratikPB2123

Omar Emara commented

2022-06-20 11:25:38 +02:00

Added subscriber: @OmarEmaraDev

Omar Emara commented

2022-06-20 11:25:38 +02:00

Changed status from 'Needs Triage' to: 'Archived'

Omar Emara closed this issue

2022-06-20 11:25:38 +02:00

Omar Emara commented

2022-06-20 11:25:38 +02:00

I don't think we can say there is an intended behavior, the behavior is just what the developer wrote the function to do, which in this case doesn't handle the default value.
As for writing a more comprehensive code in the documentation as you attached in your report. I think that the smaller example is intentional, as the documentation just wants to demonstrate the mechanism, not recreate the existing behavior.
So I don't think this is a bug in the documentation or the code. You can try to submit a patch to clarify the documentation a bit if you want, but not sure if the responsible developer would agree.

I don't think we can say there is an intended behavior, the behavior is just what the developer wrote the function to do, which in this case doesn't handle the default value. As for writing a more comprehensive code in the documentation as you attached in your report. I think that the smaller example is intentional, as the documentation just wants to demonstrate the mechanism, not recreate the existing behavior. So I don't think this is a bug in the documentation or the code. You can try to submit a patch to clarify the documentation a bit if you want, but not sure if the responsible developer would agree.

Sign in to join this conversation.

No Label

Download

What's New

Blender Studio

Manual

Developers Blog

Documentation

Benchmark

Blender Conference

Development Fund

One-time Donations

API: bpy.props getter function returns KeyError instead of default value #98939