Simple python code does not work

Question

Not sure why this simple code does not work. I tried several things... but it only works if the values are statics . In this example I put one dinamic value (does not work) and another that works but is burned.

Code:

import bpy
#create prop_group
props = {
    "name" : [],
    "type" : [],
}
#add props 
props["name"].append( "fl_prop" )
props["type"].append( "float" )
print("---" )
class CustomPropGr(bpy.types.PropertyGroup):
global props

for name in props[ "name"] :
    for type in props[ "type" ] :

        if type == "float" :
            print("debug:: name : ", name, " type: " ,type )
            name : bpy.props.FloatProperty( name = name )
        # end if

    # end for
# end for

no_dinamic_prop : bpy.props.FloatProperty( name = "test" )


end CustomPropGr
bpy.utils.register_class( CustomPropGr )
#make it enable and discovery for all objects
bpy.types.Object.custom_prop_gr = bpy.props.PointerProperty(type=CustomPropGr)
so = bpy.context.active_object
so.custom_prop_gr.no_dinamic_prop = 5.90
so.custom_prop_gr.fl_prop         = 90.5
print( "no_dinamic_prop    : ", so.custom_prop_gr.no_dinamic_prop )
#comment the below line to see the outputs
print( "dina prop (fl_prop): ", so.custom_prop_gr.fl_prop )
print("---" )

Answer 1

name : bpy.props.FloatProperty( name = name )

is assigning bpy.props.FloatProperty( name = name ) to the variable called name ( the name before the : )

Then you try to assign a value to so.custom_prop_gr.fl_prop which does not exist, because you used the variable name to create the custom property.

Then in your print command at the end:

print( "dina prop (fl_prop): ", so.custom_prop_gr.fl_prop )

is also trying to call so.custom_prop_gr.fl_prop which does not exist.

Change:

so.custom_prop_gr.fl_prop         = 90.5
print( "dina prop (fl_prop): ", so.custom_prop_gr.fl_prop )

to:

so.custom_prop_gr.name         = 90.5
print( "dina prop (fl_prop): ", so.custom_prop_gr.name )

Answer 2

Use Python's type method for dynamic props

Recommend using python's type for dynamically creating classes.

Here is an example.

• Set up two float properties "foo" and "bar" in our props dictionary. Both are given "float" as a type. Have converted to bpy prop by simply making it title case "Float" and tacking "Property" to the end, then grabbing that type via get attribute from bpy.props.

• For the non dynamic members have set up some class to define these.

• Then using type create a class, give it the name we wish to define, the inherited classes, lastly PropertyGroup.

• Finally The annotations, ie our dynamic props are added in the last argument.

Test script.

import bpy
from bpy.props import (
        PointerProperty,
        FloatProperty,
        )
from bpy.types import PropertyGroup
props = {"foo" : "float",
         "bar" : "float",
         }
class NonDynamic:
    test : FloatProperty(name="Bar")
Group = type(
        "CustomPropGr",
        (NonDynamic, PropertyGroup,),
        {'annotations' :
            {
            k : getattr(bpy.props, f"{v.title()}Property")(name=k)
            for k, v in props.items()
        }
    }
)


bpy.utils.register_class(Group)
bpy.types.Object.foobar = PointerProperty(type=Group)

Test run python console.

>>> C.object
bpy.data.objects['Cube']
>>> C.object.foobar
bpy.data.objects['Cube'].foobar
>>> str(C.object.foobar)
'<bpy_struct, CustomPropGr("") at 0x7f5b1a793f68>'
>>> C.object.foobar.foo
0.0
>>> C.object.foobar.bar
0.0
>>> C.object.foobar.test
0.0

Notes: can see from this can extend this quite simply to create a method that dynamically creates classes. I often use this to create AddonPreferences class from the addons underlying modules.

Have used a dictionary instead of the two separate lists for name and type, if using the two lists suggest using zip

for k, v in zip(props["name"], props["type"]):
    ...

Related:

Blender 2.8 - Field property declaration and dynamic class creation