you can use getter/setter functions for these kind of updates or can check them in modal functions by checking left clicks.

an example of getter/setter functions is described in API like below:

import bpy


# Simple property reading/writing from ID properties.
# This is what the RNA would do internally.
def get_float(self):
    # do some stuff here before get
    return self.myfloat

# self in this method is the object which you attach the property to
# in this case self is any scene in bpy.data for example bpy.data.scenes[0]
def set_float(self, value):
    # do some stuff here before/after set because no return is required
    self.myfloat = value


bpy.types.Scene.myfloat = bpy.props.FloatProperty(get=get_float, set=set_float)

now whenever you get/set a scene.myfloat data above methods work.

you can use getter/setter functions for these kind of updates or can check them in modal functions by checking left clicks.

an example of getter/setter functions is described in API like below:

import bpy


# Simple property reading/writing from ID properties.
# This is what the RNA would do internally.
def get_float(self):
    # do some stuff here before get
    return self.get("myfloat",0.0)

# self in this method is the object which you attach the property to
# in this case self is any scene in bpy.data for example bpy.data.scenes[0]
def set_float(self, value):
    # do some stuff here before/after set because no return is required
    self["myfloat"] = value


bpy.types.Scene.myfloat = bpy.props.FloatProperty(get=get_float, set=set_float)

now whenever you get/set a scene.myfloat data above methods work.