Refactoring cached (lazy) property methods in metamodel classes

Many metamodel classes have property methods of this repeating pattern:

def fun(self):
    if not hasattr(self, '__prop'):
        ...
    return self.__prop

where __prop is __value, __type or __func. We can save upto two lines of code per function if we use a decorator function like this:

def cached(func, prop):
    def _cached_func(*args, **kwargs):
        return getattr(args[0], prop) if hasattr(args[0], prop) else func(*args, **kwargs)
    return _cached_func

@cached('__value')
def fun(self):
    ...

Alternatively use @cached_property decorator instead of @property as it is currently. The cached_property is in available in Python >= 3.8 in the functools package.