[Python-Dev] PEP 492: async/await in Python; v3

[Yury Selivanov]

On 2015-04-29 5:13 AM, Greg Ewing wrote:
> Yury Selivanov wrote:
>
>> 3. GenObject __iter__ and __next__ raise error
>> *only* if it has CO_NATIVE_COROUTINE flag.  So
>> iter(), next(), for..in aren't supported only
>> for 'async def' functions (but will work ok
>> on asyncio generator-based coroutines)
>
> What about new 'async def' code called by existing
> code that expects to be able to use iter() or
> next() on the future objects it receives?
>
>> 4. 'yield from' *only* raises an error if it yields a
>> *coroutine with a CO_NATIVE_COROUTINE*
>> from a regular generator.
>
> Won't that prevent some existing generator-based
> coroutines (ones not decorated with @coroutine)
> from calling ones implemented with 'async def'?
>
It would.  But that's not a backwards compatibility
issue.

Everything will work in 3.5 without a single line
change.  If you want to use new coroutines - use
them, everything will work too.

If, however, during the refactoring you've missed
several generator-based coroutines *and* they are
not decorated with @coroutine - then yes, you will
get a runtime error.  I see absolutely no problem
with that.  It's a small price to pay for a better
design.

Yury