[Python-Dev] Musings on concurrency and scoping ("replacing" Javascript)

[Ka-Ping Yee]

On Thu, 6 Jul 2006, Phillip J. Eby wrote:
> As much as I'd love to have the nested scope feature, I think it's only
> right to point out that the above can be rewritten as something like this
> in Python 2.5:
>
>      def spam():
>          local_A = do_work()
>          result_1 = yield do_network_transaction()
>          local_B = do_work(result_1)
>          result_2 = yield do_network_transaction()
>          do_work(local_A, local_B, result_1, result_2)
>          ...
>
> All you need is an appropriate trampoline (possibly just a decorator) that
> takes the objects yielded by the function, and uses them up to set up
> callbacks that resume the generator with the returned result.

Clever!  Could you help me understand what goes on in
do_network_transaction() when you write it this way?  In the
Firefox/JavaScript world, the network transaction is fired off
in another thread, and when it's done it posts an event back
to the JavaScript thread, which triggers the callback.

And what happens if you want to supply more than one continuation?
In my JavaScript code i'm setting up two continuations per step --
one for success and one for failure, since with a network you never
know what might happen.


-- ?!ng