[Python-ideas] Cofunctions - an enhancement to yield-from

Greg Ewing greg.ewing at canterbury.ac.nz
Mon Aug 2 11:34:25 CEST 2010

Bruce Leban wrote:

>     The only special consideration is that 'codef' must be used to define
>     any function that directly or indirectly calls another cofunction.
> It seems to me that this is a big requirement. If a module that I'm 
> using uses cofunctions, then every use of that module must be a 
> cofunction all the way up to my main function.

Well, at least all the way up to the coroutine scheduler or
driver or whatever you want to call it.

That statement is actually a bit abbreviated. The caller
doesn't strictly have to be a cofunction, but if it's not,
it has to be aware that the called cofunction is a generator
and deal with it as such, for example by using 'yield from'
(which in turn makes the caller a generator) or by looping
over it (in which case the caller can be an ordinary

However you arrange things, there has to be an unbroken
chain of generators from the main loop driving the coroutines
down to the functions containing the yields. The only question
is whether to mark them as such at the function level (using
'codef') or at the call site level (using 'yield from').

> Worse, I wouldn't be able to change the implementation of a module to 
> use cofunctions because it will break the current users.

There would be nothing to stop a module from using cofunctions
internally, as long as it runs its own driver loop and presents
its outside interface in the form of ordinary functions that
run to completion.

But if it exposes any cofunctions directly to its users, they
will need to be aware of the fact, just as they need to be
aware of an exposed function that is a generator.


More information about the Python-ideas mailing list