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Comment by shanemhansen | Hacker News Reader

Great article. I had the misfortune of writing a bunch of twisted code over a decade ago and I wanted to remind the author that twisted has a feature called "inline callbacks" that allow you to use yield. https://twisted.org/documents/16.4.1/core/howto/defer-intro....

So twisted code can actually look like:

    @inlineCallbacks
    def doIt():
        responseBody = yield makeRequest("GET", "/users")
        returnValue(json.loads(responseBody))

iirc `returnValue` throws an exception of a specific type. It's ugly, but it's also the logical implementation of async on top of yield/generators.

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This is so nostalgic. I actually met my cofounder on github due to a discussion on twisted vs gevent back in 2011. I had my inital code in twisted and he wrote the gevent piece. Fast forward 12 years and we still use gevent at http://plivo.com :)

Some of our initial code snippets:

# Twisted

def __protocolSendRaw(self, name, args=""): deferred = defer.Deferred() self.__EventQueue.append((name, deferred)) self.rawSend("%s %s" % (name, args)) return deferred

# Gevent

def _protocol_sendmsg(self, name, args=None, async=False): if self._closing_state: return Event() _async_res = gevent.event.AsyncResult() _uuid, event = _async_res.get() return event

Off topic: PLIVO, the norwegian term actually is a protocol used by critical services here. Thought you might find it interesting :)

> PLIVO (an abbreviation for ongoing life-threatening violence) is a procedure for cooperation between the police, the fire service, the rescue service and the healthcare system in incidents where life-threatening violence is perpetrated against several people.

Nice, did not know this.. Plivo in latvian means flying high, thats was one of the languages we named it based on.

damn i had memories of using plivo back in 2012 2013 2014

returnValue raises a specific exception that inlineCallbacks understands and translates to a normal return value. It was a hack that was only needed for python versions that couldn't have generators return non-None values. With modern versions, you don't need it anymore -- just use return.

My last job (2019 - 2022) was in part shepherding a 2013-era Python 2 Tornado-and-Motor (yes the async implementation of the MongoDB driver for Python) application into Python 3 and such modern niceties.

Absolutely fuck yield-raise based async implementations. Just remembering those induces psychic damage; implementing async as a massive hack on top of the language is impressive but also the kind of thing we're going to whisper to junior engineers as scary campfire stories for DECADES.

While inlineCallbacks exists, and indeed works, I would recommend not using it. I recall it not interacting with mypy particularly well, and in general being such a hack it had some annoying sharp edges. Explicit callbacks might be annoying but at least they are extremely clear on what's happening.

Nowadays twisted supports this syntax:

    async def doIt():
        responseBody = await makeRequest("GET", "/users")
        return json.loads(responseBody)

See https://patrick.cloke.us/posts/2021/06/11/converting-twisted...

Also, asyncio started like this as well.

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