How do I prevent an infinite loop on property update?

Question

I'm displaying N-instances of a Collection Property (depending on the amount of selected objects) — the values are floats, default values are 100/N, and I want to be able to recalculate values of other properties when one of the instance is changed so that a sum would be always 100 — basically I want to have something like influence between objects limited by 100(%).

Here's how it looks: in this example two other fields should be 25 and 25

I tried to use the update function and change "other values" (instances that aren't the active) but I guess since every instance uses the same function Blender goes in infinite recursion and crashes. Maybe my approach is wrong and I should do this in a different way?

import bpy
import math
def update_float(self,context):
    other_props = [prop for prop in context.scene.my_custom_set if prop.name != self.name]
    rest = 100 - self.value
    for prop in other_props:
        prop.value = rest / len(context.selected_objects) # crashes blender
class SceneSettingItem(bpy.types.PropertyGroup):
    name: bpy.props.StringProperty(name="Obj Name", default="")
    value: bpy.props.FloatProperty(name="Z coord", default=0, max=100, min=0, update=update_float)
class SimpleOperator2(bpy.types.Operator):
    """"""
    bl_idname = "object.simple_operator_sk"
    bl_label = "Collection Property Test 2"
    bl_options = {'REGISTER', 'UNDO'}
def draw(self, context):
    layout = self.layout

    for my_item in context.scene.my_custom_set:
        row = layout.row()
        row.prop(my_item, "value", text=f"Prop for {my_item.name}")

def execute(self, context):
    return {'FINISHED'}

def invoke(self, context, event):
    context.scene.my_custom_set.clear()
    for ob in context.selected_objects:
        my_item = context.scene.my_custom_set.add()
        my_item.name = ob.name
        my_item.value = math.ceil(
            10000 / len(context.selected_objects))/100

    return context.window_manager.invoke_props_dialog(self)



def register(): 
    bpy.utils.register_class(SimpleOperator2)
    bpy.utils.register_class(SceneSettingItem)
    bpy.types.Scene.my_custom_set = bpy.props.CollectionProperty(type=SceneSettingItem)
def unregister():
    del bpy.types.Scene.my_custom_set
    bpy.utils.unregister_class(SimpleOperator2)
    bpy.utils.unregister_class(SceneSettingItem)
if name == "main":
    register()

Answer 1

Set the custom property.

Internal "get/set" function of property?

Why does an update function loop when string property is reset?

When a property defined via bpy.props is set to non default, it is saved on the object as a custom property, eg setting ob.foo = 33 is equivalent of ob["foo"] = 33. Setting the property data does not fire the update,

... hence can set the others by custom property.

Have removed name since it is added to a collection item by default

In the method self is the instance of the collection item, can test against this rather than name. self.id_data is the scene, since this is the ID object the collection is defined on.

import bpy
import math
def update_float(self,  context):
    other_props = [prop for prop in self.id_data.my_custom_set if prop != self]
    v = (100 - self.value) / len(other_props)
    for p in other_props:
        p["value"] = v
class SceneSettingItem(bpy.types.PropertyGroup):
    value: bpy.props.FloatProperty(name="Z coord", default=0, max=100, min=0, update=update_float)
class SimpleOperator2(bpy.types.Operator):
    """"""
    bl_idname = "object.simple_operator_sk"
    bl_label = "Collection Property Test 2"
    bl_options = {'REGISTER', 'UNDO'}
def draw(self, context):
    layout = self.layout

    for my_item in context.scene.my_custom_set:
        row = layout.row()
        row.prop(my_item, "value", text=f"Prop for {my_item.name}")

def execute(self, context):
    return {'FINISHED'}

def invoke(self, context, event):
    context.scene.my_custom_set.clear()
    for ob in context.selected_objects:
        my_item = context.scene.my_custom_set.add()
        my_item.name = ob.name
        my_item.value = math.ceil(
            10000 / len(context.selected_objects))/100

    return context.window_manager.invoke_props_dialog(self)



def register(): 
    bpy.utils.register_class(SimpleOperator2)
    bpy.utils.register_class(SceneSettingItem)
    bpy.types.Scene.my_custom_set = bpy.props.CollectionProperty(type=SceneSettingItem)
def unregister():
    del bpy.types.Scene.my_custom_set
    bpy.utils.unregister_class(SimpleOperator2)
    bpy.utils.unregister_class(SceneSettingItem)
if name == "main":
    register()
    bpy.ops.object.simple_operator_sk('INVOKE_DEFAULT')

PS. Will be issues with number of selected objects being one or less, resolve by polling panel and or operator as true only when 2 or more objects are selected.

Poll method for custom panel