On 2015-05-02 2:14 PM, Ethan Furman wrote:
On 05/02, Yury Selivanov wrote:
On 2015-05-02 1:04 PM, Ethan Furman wrote:
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.
Because we don't want 'await' to accept random generators.
It can't do anything meaningful with them, in a world where
all asyncio code is written with new syntax, passing generator
to 'await' is just a bug.
And yet in current asyncio code, random generators can be accepted, and not
even the current asyncio.coroutine wrapper can gaurantee that the generator
is a coroutine in fact.
This is a flaw in the current Python that we want to fix.
For that matter, even the new types.coroutine cannot gaurantee that the
returned object is a coroutine and not a generator -- so basically it's just
there to tell the compiler, "yeah, I really know what I'm doing, shut up and
do what I asked."
Well, why would you use it on some generator that is not
a generator-based coroutine?
'types.coroutine' is something that we need to ease transition
to the new syntax.
This doesn't make sense -- either the existing generators are correctly
returning coroutines, in which case the decorator adds nothing, or they
are returning non-coroutines, in which case the decorator adds nothing.
So either way, nothing has been added besides a mandatory boiler-plate
requirement.
It's not nothing; it's backwards compatibility. Please read
https://www.python.org/dev/peps/pep-0492/#await-expression
@types.coroutine marks generator function that its generator
is awaitable.
Yury
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