def walk(self, callback, collect=None):
        """
        Executes callback on all the subtree starting at self.
        returns a list of all return values that are not ``None``.

        Arguments:
            callback (a function):
                Callable that takes a :class:`CocosNode` as an argument.
            collect (list):
                List of non-`None` returned values from visited nodes.

        Returns:
            list: The list of non-`None` return values.

        """
        if collect == None:
            collect = []

        r = callback(self)
        if r is not None:
            collect.append(r)

        for node in self.get_children():
            node.walk(callback, collect)

        return collect
dataset/ETHPy150Open los-cocos/cocos/cocos/cocosnode.py/CocosNode.walk/operator `is` -> `==`