wip python attempt at creating object with dynamic props

reactive.py

import inspect

def Reactive(obj):

    class ReactiveObject(object):
        def __init__(self, obj, storage):
            self.storage = storage
            self.obj = obj

        def on_change(self, key, newValue, prevValue):
            if 'on_change' in self.obj[key]:
                fn = self.obj[key]['on_change']
                ln = len(inspect.signature(fn).parameters)
                if ln == 0:
                    fn()
                elif ln == 1:
                    fn(newValue)
                elif ln == 2:
                    fn(newValue, prevValue)
            else:
                print(key, newValue, prevValue) 

    storage = {} 

    def create_fget(key):
        def fget(self):

            val = self.storage[key]

            if 'fget' in self.obj[key]:
                return self.obj[key]['fget'](val)
            else:
                return val
        return fget

    def create_fset(key):
        def fset(self, newValue):
            currentValue = self.storage[key]
            if currentValue != newValue:
                if 'fset' in self.obj[key]:
                    self.obj[key]['fset'](val)
                else:
                    self.storage[key] = newValue
                print(self.storage[key])
                self.on_change(key, newValue, currentValue)
        return fset  


    for key,item in obj.items():
       
        storage[key] = item['value']
        fget = create_fget(key)
        fset = create_fset(key) 
        prop = property(fget, fset)
        setattr(ReactiveObject, key, prop)

    return ReactiveObject(obj, storage) 
            


a = Reactive({  
    'a':{

        'value':3,
        'fget':lambda val:val+1,
        'on_change':lambda : print('oooh') 
        
    },
    'b':{
        'value':'hello',
        'on_change':lambda x, y: print('oh', x, y)
    } 
})

print(a.a == 4)
print(a.b == 'hello') 
a.a = 8