Make StreamingResponse compatible with normal iterators

[tiangolo]

Make StreamingResponse compatible with normal iterators.

Continuing from #457, #457 (comment)

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I also removed the mention to iterator_to_async from the docs, only mention that it supports both async and normal generators.

I'd also be interested in if there's any nice ways around we could use something like this and drop aiofiles [...]

Let's see what do you think about this one and then I'll take a stab at that 😄

[lovelydinosaur]

How about iterate_in_threadpool to mirror run_in_threadpool.

[tiangolo]

Great idea. I struggled a lot to name it and wasn't quite convinced either.

[lovelydinosaur]

Do we strictly need the _StopSyncIteration indirection?

[lovelydinosaur]

Can we not catch StopIteration directly?

[tiangolo]

StopIteration is used internally by coroutines, it was used before to yield values, here's a short summary in the PEP: https://www.python.org/dev/peps/pep-0492/#why-stopasynciteration

I can think of an alternative using classes, based on this example: https://www.python.org/dev/peps/pep-0492/#example-2, would you prefer that?

[tiangolo]

Because StopIteration was used to yield values, catching it directly in iterate_in_threadpool is not possible, it is converted to a RuntimeError.

Actually, now that I think of it, using a class would still need the indirection, as we need an exception that is propagated up/out even when run inside of run_in_threadpool.

[lovelydinosaur]

👍 Released as prerelease version 0.12.0b3

[tiangolo]

Awesome! Thanks! 🎉 🚀