I don't like the idea, because a + b should produce new list c without modification of both. Which is not memory optimal and cost of it is not obvious. Also dic

I don't like the idea, because a + b should produce new list c without modification of both. Which is not memory optimal and cost of it is not obvious. Also dict is used a lot for sub classes and that could break a lot of existing functionality with potentially no benefit for most of the developers. I don't think that merging is very common operation for dicts and even so it could be done with 1 or 2 update function calls, but that will be obvious in that case, while '+' in deeps of duck typing code is not. Also absence of '+' operation for dicts is kind of guard for type validation in case if someone passed dict instead of integer. Which is pretty common when you parse some JSON from client.