def __set__(self, obj, value):
        if '_lazy_fields' in obj.__dict__:
            # initialize storage for lazy fields
            obj.__dict__['_lazy_fields'] = {}
        if self.field.name in obj.__dict__:
            # remove old converted values
            del obj.__dict__[self.field.name]
        obj.__dict__['_lazy_fields'][self.field.name] = value