def _get_field_class(self, class_str):
        """Import and return the field class.

        Given the module path to a field class in class_str, imports the class
        and returns it. If class_str does not specify a valid field class, an
        exception is raised.
        """
        field_class = self._get_class(class_str)

        if not issubclass(field_class, Field):
            raise TypeError(class_str % '%s is not a Field class.')

        return field_class
dataset/ETHPy150Open reviewboard/ReviewBot/extension/reviewbotext/forms.py/ProfileForm._get_field_class/swapped operands of `%`