def __get__(self, obj, type=None):
        if obj is None:
            raise AttributeError('Can only be accessed via an instance.')
        if not obj.__dict__.has_key(self.field.name):
            # do lazy conversion now
            obj.__dict__[self.field.name] = self.field.to_python(obj.__dict__['_lazy_fields'][self.field.name])

        return obj.__dict__[self.field.name]