Find all the nodes of a given type.  If the type is a tuple,
        the check is performed for any of the tuple items.

def find_all(self, node_type):
        """Find all the nodes of a given type.  If the type is a tuple,
        the check is performed for any of the tuple items.
        """
        for child in self.iter_child_nodes():
            if isinstance(child, node_type):
                yield child
            for result in child.find_all(node_type):
                yield result