Callbacks as our Generation's Goto Statement

Re:Callbacks as our Generation's Goto Statement by lambda on Thursday August 15, 2013 @07:17PM (#6221210)

You get a similar interface in Python's Twisted using the @inlineCallbacks decorator:

    @inlineCallbacks
    def example():
        try:
            obtain_some_lock()
            ui_status("Fetching file...")
            result = yield fetch_file_from_server(args)
            ui_status("Uploading file...")
            yield post_file_to_other_server(result)
            ui_status("Done.")
        except SomeError as e:
            ui_status("Error: %s" % e.msg)
        finally:
            release_some_lock()

I must say that this style of writing async code is much friendlier than descending into callback hell.

There is work to make a similar async interface native in Python 3, in PEP 3156 http://www.python.org/dev/peps/pep-3156/, so this should become more widely available even to those who don't use Twisted.

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Re:Callbacks as our Generation's Goto Statement by rosh on Thursday August 15, 2013 @09:18PM (#6221659)

Tornado has a similar interface:

    class GenAsyncHandler(RequestHandler):
        @gen.coroutine
        def get(self):
            http_client = AsyncHTTPClient()
            response = yield http_client.fetch("http://example.com")
            do_something_with_response(response)
            self.render("template.html")

(via http://www.tornadoweb.org/en/stable/gen.html ..)

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Re:Callbacks as our Generation's Goto Statement by obiterdictum on Thursday August 15, 2013 @09:23PM (#6221673)

Obligatory mention of gevent[1].

It handles all the plumbing for you with monkey-patching I/O calls. No annotations necessary, you just write linear code.

[1] http://www.gevent.org

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Re:Callbacks as our Generation's Goto Statement by ak217 on Thursday August 15, 2013 @07:39PM (#6221306)

Yes! I really hope this use of yield will bubble up to the language spec and become pervasive in Python. It really strikes me as the Pythonic approach to solving callback hell.

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Re:Callbacks as our Generation's Goto Statement by masklinn on Friday August 16, 2013 @03:41AM (#6222680)

> Yes! I really hope this use of yield will bubble up to the language spec and become pervasive in Python.

And the time machine spaketh: http://www.python.org/dev/peps/pep-3156/#coroutines-and-the-...

(it has no reason to "bubble up to the language spec", the language provides all the right primitives — especially with Python 3's `yield from`, it's up to the libraries to use them. That is a Good Thing.)

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Re:Callbacks as our Generation's Goto Statement by ak217 on Friday August 16, 2013 @12:22PM (#6224968)

Good point. Bubble up to the standard library, then.

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Re:Callbacks as our Generation's Goto Statement by danabramov on Thursday August 15, 2013 @07:22PM (#6221228)

That's very cool, thanks for sharing.

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