The [types.coroutine] function applies CO_COROUTINE flag to
generator-function's code object, making it return a coroutine
Further down in https://www.python.org/dev/peps/pep-0492/#id32:
[await] uses the yield from implementation with an extra step of
validating its argument. await only accepts an awaitable,
which can be one of:
- A generator-based coroutine object returned from a generator
decorated with types.coroutine().
If I'm understanding this correctly, type.coroutine's only purpose is to add
a flag to a generator object so that await will accept it.
This raises the question of why can't await simply accept a generator
object? There is no code change to the gen obj itself, there is no
behavior change in the gen obj, it's the exact same byte code, only a
flag is different.
types.coroutine feels a lot like unnecessary boiler-plate.