AttributeError: can't add special method to already-subclassed class

[pinqwing]

I am getting this error in microPython (not in cPython) and I don't have a clue:

AttributeError: can't add special method to already-subclassed class

The offending line is:

    @classmethod
    def _addDynamicProperty(cls, propName, getter, setter):
        if not cls._dynamicProperties:
            # force per class instances
            cls._dynamicProperties = []

        if not hasattr(cls, propName):
            setattr(cls, propName, property(getter, setter))   <--- HERE --------------
            cls._dynamicProperties.append(PropDef(propName, getter, setter))

[peterhinch]

I don't know the answer, but you might get some clues from differences to cPython.

[pinqwing]

Indeed, it is the first time I used __new__in uP, so I was not aware of difference #3 and its warning. Thanks.