Turning a callback function into a generator

[Alex Martelli]

Lawrence D'Oliveiro <ldo at geek-central.gen.new_zealand> wrote:

> In article <44a89559 at nntp0.pdx.net>,
>  Kirk McDonald <kirklin.mcdonald at gmail.com> wrote:
> 
> >I want to somehow, in some way, provide an iteration interface to this
> >function. Thoughts?
> 
> Run it in a separate thread/process?

Sounds best to me.  Specifically, given (e.g.) something like the OP's

def func(callback):
     for i in [1, 2, 3, 4, 5]:
         callback(i)

we might have a wrapper such as:

import thread
import Queue

def wrap_cb_into_gen(func):
    q = Queue.Queue(1)           # maximum size of 1
    def callback(item):
        q.put(item)
    all_done_sentinel = object()
    def thread_skeleton():
        func(callback)
        q.put(all_done_sentinel)
    thread.start_new_thread(thread_skeleton, ())
    while True:
        item = q.get()
        if item is all_done_sentinel: break
        yield item


Of course, there are lighter-weight options than a length-1 Queue for
the purpose of synchronizing these two threads, but I always tend to
prefer Queue (for its simplicity, generality, solidity) to other
synchronization structures and architectures, unless there is some very
strong reason to do otherwise in a specific case.  Also, I normally use
module threading rather than the lower-level module thread -- here,
clearly, either one will do just fine.


Alex