Expose binary operations (*, &, etc.)

[alex]

These are available in the CPython API via PyNumber_And, PyNumber_Multiply, etc.

I'm happy to send PRs for these. Though a) it probably makes sense to do this after #3684, b) is there a better way to do this than dozens of new methods on PyAny? (https://docs.python.org/3/c-api/number.html)

[davidhewitt]

I would support having these, I've needed a couple of them in the past but just used the raw ffi instead of getting around to figuring out how to expose them properly 🙈

I think #3684 probably isn't blocking you. Maybe even just add the new methods only to the PyAnyMethods trait? It might be a nice carrot for users to upgrade 😃

I haven't thought of a better way than to add methods for each operator.

The usual problem with rust operators and traits is that we cannot express fallibility. I suppose for some of these we might be able to control the return value, does it make sense for + to return PyResult<Bound<PyAny>>? I think ((a + b)? + c)? is somewhat clunky to write, a.add(b)?.add(c)? might be clearer anyway?