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[Python-ideas] Cofunctions - Back to Basics

Christian Tismer tismer at stackless.com
Sat Oct 20 17:59:41 CEST 2012 
Picking that up, too...

On 29.10.11 09:37, Greg Ewing wrote:
> Nick Coghlan wrote:
>
>> The limitation of Lua style coroutines is that they can't be suspended
>> from inside a function implemented in C. Without greenlets/Stackless
>> style assembly code, coroutines in Python would likely have the same
>> limitation.
>>
>> PEP 3152 (and all generator based coroutines) have the limitation that
>> they can't suspend if there's a *Python* function on the stack. Can
>> you see why I know consider this approach categorically worse than one
>> that pursued the Lua approach?
>
> Ouch, yes, point taken. Fortunately, I think I may have an
> answer to this...
>
> Now that the cocall syntax is gone, the bytecode generated for
> a cofunction is actually identical to that of an ordinary
> function. The only difference is a flag in the code object.
>
> If the flag were moved into the stack frame instead, it would
> be possible to run any function in either "normal" or "coroutine"
> mode, depending on whether it was invoked via __call__ or
> __cocall__.
>
> So there would no longer be two kinds of function, no need for
> 'codef', and any pure-Python code could be used either way.
>
> This wouldn't automatically handle the problem of C code --
> existing C functions would run in "normal" mode and therefore
> wouldn't be able to yield. However, there is at least a clear
> way for C-implemented objects to participate, by providing
> a __cocall__ method that returns an iterator.
>

What about this idea?
I think I just wrote exactly the same thing in another thread ;-)

Is it still under consideration?

(I missed quite a lot when recovering from my strokes ...)

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