migrate @gen.coroutine AsyncHTTPClient and Motor to native python-3-5-async-and-await

[dziz...@gmail.com]

Hi!

I'm working with latests Tornadoweb 4.4.1 and python 3.5 and motor '0.6.2'. I'm intensively use tornado.curl_httpclient.CurlAsyncHTTPClient and Motor Mondodb client.

What would be the benefit to migrate all migrate @gen.coroutine native python-3-5-async-and-await 

http://www.tornadoweb.org/en/stable/guide/coroutines.html#python-3-5-async-and-await

Is it risky, worth? Any ideas.

Thanks!

[A. Jesse Jiryu Davis]

Not risky, Tornado and Motor support async / await very well. You can convert generator-based coroutines to native coroutines one at a time, since Tornado works with a mix of the two styles:

from tornado import gen

from tornado.ioloop import IOLoop

from tornado.locks import Condition

condition = Condition()

@gen.coroutine

def decorated():

    yield gen.sleep(1)

    print("decorated")

    return 1

async def modern():

    result = await decorated()

    print("modern")

    return result

@gen.coroutine

def outer():

    result = yield modern()

    print("outer")

    return result

print(IOLoop.current().run_sync(outer))

Is it worth the trouble? The async / await syntax is nicer and faster. If you use Motor's "cursor.fetch_next" a lot, you might see a measurable performance improvement:

https://emptysqua.re/blog/motor-0-5-beta-asyncio-async-await/#async-and-await

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[dziz...@gmail.com]

Thanks! I'll give it a try.

I've seen in your code:

from tornado.locks import Condition

what is the purpose of using it?

I wander, because recently I'm strugling with duplicates in mongo (yielding list of functions and each one might insert same data). I'm creating unique indexes, but then I have to handle DuplicateKeyError exception.

Would Condition be usefull in this case?

[A. Jesse Jiryu Davis]

I think Condition is too complex for what you need. You have multiple functions inserting the same data sometimes, and that's normal expected behavior for your application? If so you can just catch the error:

try:

    yield collection.insert(doc)

except DuplicateKeyError:

    pass   # Don't care.

Another option is upsert to only insert a document once, then update it if it's already there.

https://docs.mongodb.com/manual/reference/method/db.collection.update/#upsert-option

[dziz...@gmail.com]

Yes, unfortunately remote API I'm using might deliver duplicates, especially when fetched in number of coroutines. I'll proceed with DuplicateKeyError.

Thank you!

[A. Jesse Jiryu Davis]

Cool. What are you making? I'm always curious about Motor users. 

[dziz...@gmail.com]

what about yielding lists:

I've implemented in several places: http://www.tornadoweb.org/en/stable/gen.html

response1, response2 = yield [http_client.fetch(url1),
                                  http_client.fetch(url2)]

while awaiting I'm getting: TypeError: object list can't be used in 'await' expression

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[Ben Darnell]

With `await`, lists must be wrapped in `tornado.gen.multi`:

    response1, response2 = await gen.multi([http_client.fetch(url1), http_client.fetch(url2)])

[dziz...@gmail.com]

works like a charm!

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