Just found an interesting example explaining how that works, I wasn't aware of it either (this site also has nice 'yield from' explainer):

https://lerner.co.il/2020/05/08/making-sense-of-generators-c...

> "The above code looks a bit weird, in that “yield’ is on the right side of an assignment statement. This means that “yield” must be providing a value to the generator. Where is it getting that value from?

Answer: From the “send” method, which can be invoked in place of the “next” function. The “send” method works just like “next”, except that you can pass any Python data structure you want into the generator. And whatever you send to the generator is then assigned to “x”."

Knew about it, but didn't quite understand how to use send until I read through the link you posted. Thanks for that!

Regarding that article specifically I think it could've done better service to 'yield from' had it mentioned recursive generators. One example would be flattening nested lists: have a flatten function that checks if its argument is iterable: if not just yield the thing else yield from flatten for every item in the iterable.

Back in the days before async/await, twisted (an asynchronous I/O framework) used these to emulate async/await -- you could yield a differed value (like a promise/future), and it would pass it back when the value was available, saving some effort making your state explicit and writing many callbacks:

https://twisted.org/documents/21.2.0/api/twisted.internet.de...

I used this in AoC for the first time a couple of years ago, as a consequence of diving deeply into asyncio. https://explog.in/static/aoc2019/AoC23.html

I'm glad to see someone with the same idea was able to take it to completion. Life got in the way for me and I never got to implement that part. If I ever get back around to it I will consult your solution if I get stuck.