        def get_field(self, field_name, args, kwargs):
            first, rest = formatter_field_name_split(field_name)
            obj = self.get_value(first, args, kwargs)
            for is_attr, i in rest:
                if is_attr:
                    obj = self._env.getattr(obj, i)
                else:
                    obj = self._env.getitem(obj, i)
            return obj, first
The software uses a function that accepts a format string as an argument, but the format string originates from an external source.