def check_classes(self, scope=-1):
        """ Check if pending identifiers are defined or not. If not,
        returns a syntax error. If no scope is given, the current
        one is checked.
        """
        for entry in self[scope].values():
            if entry.class_ is None:
                syntax_error(entry.lineno, "Unknown identifier '%s'" % entry.name)
Check if pending identifiers are defined or not. If not,
        returns a syntax error. If no scope is given, the current
        one is checked.