Add asyncio event loop support

[takluyver]

This probably needs quite a bit of work, but it's working for a basic example, and I wanted to communicate early. @techdragon talked me into working on this at the PyCon sprints.

Asyncio is part of the standard library in Python 3.4. It's a rather similar API to tornado, so I copied and pasted the net_tornado code that's already in rethinkdb and modified it until it works. The syntax is only valid on Python 3, but the module shouldn't be imported until you do r.set_loop_type('asyncio'), so that shouldn't be a problem.

Here's the asyncio version of the tornado example from your async drivers blog post (BTW, that example is missing a colon on the while line):

import asyncio
import rethinkdb as r

r.set_loop_type("asyncio")

@asyncio.coroutine
def print_changes():
    conn = yield from r.connect(host="localhost", port=28015)
    feed = yield from r.table("tv_shows").changes().run(conn)
    while (yield from feed.fetch_next()):
        change = yield from feed.next()
        print(change)

loop = asyncio.get_event_loop()
loop.run_until_complete(print_changes())

[danielmewes]

That's really cool, thanks a lot for the pull request @takluyver !

@Tryneus I think this is one for you to review. Can you take a look when you find the time?

@takluyver Have you signed our CLA yet? http://rethinkdb.com/community/cla/

[Tryneus]

This should be asyncio, not Tornado - and the gen.Return(None) thing isn't quite true when using yield from.

[takluyver]

I think the same problem would still arise - return foo in a coroutine still works by raising StopIteration(foo), I believe. I'll update the comment.

[Tryneus]

@takluyver, thanks for putting this up, it looks great, although I made a few comments/suggestions.

[takluyver]

Thanks, I was fully expecting that it wouldn't be quite right. I'll respond to comments inline.

@danielmewes I just went and signed the CLA now. The address field mentioned that you might send me something - if that's a t-shirt, then save yourselves the postage, because I already picked up two at PyCon. ;-)

[danielmewes]

Good to know about the shirts @takluyver :)

[Tryneus]

Is there a reason these tests are commented out? Were they taking too long? If I remember correctly they're the longest-running tests in the suite.

[takluyver]

Oh, I was commenting out chunks of the tests just so that I could run them quickly. I didn't mean to commit them commented out.

[takluyver]

Tests are now uncommented and passing, and I think I've addressed all of the review comments so far.

[Tryneus]

Awesome, looks great, @takluyver! Merging this into next, it should make it into the 2.1 release. I'll try to get more tests in for the alternate net.py implementations before then.

Thanks for all the help!

[takluyver]

You're welcome :-)