[Python-Dev] yield back-and-forth?

[Nick Coghlan]

Nick Coghlan wrote:
> Exception propagation is a different story. What do you want to propagate? All 
> exceptions from the body of the for loop? Or just those from the yield statement?
> 
> Well, isn't factoring out exception processing part of what PEP 343 is for?

>    # We can even limit the propagated exceptions to those
>    # from the outside world and leave the rest alone
>    def main_generator():
>        ...
>        gen = sub_generator()
>        for value in gen:
>            with throw_to(gen):
>                input = yield value
>            continue input

A point I should have made here (but didn't, despite using it in a later 
example) is that the "with" versions don't allow the nested generator to 
suppress the exception.

A small refinement to gen.throw() that makes the first argument optional 
(similar to the raise statement itself) would make it straightforward to allow 
the generator to suppress passed in exceptions:

    def main_generator():
        ...
        gen = sub_generator()
        for value in gen:
            try:
                input = yield value
            except:
                gen.throw() # Default to sys.exc_info(), just like raise
            continue input

Cheers,
Nick.

-- 
Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia
---------------------------------------------------------------
             http://www.boredomandlaziness.org