Extract types (names) for typed fields (with format/type part).

        :param schema: Parser schema/format to use.
        :return: Generator for type names (as string).

def extract_types(cls, schema):
        """Extract types (names) for typed fields (with format/type part).

        :param schema: Parser schema/format to use.
        :return: Generator for type names (as string).
        """
        for field in cls.extract_fields(schema):
            if field.has_format:
                yield field.format_spec.type