asyncio - deep dive

Transcript

1. asyncio
   the exciting world of concurrent Python coroutines…
   Jacob Tomlinson
   

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2. https://opsdroid.github.io
   

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3. Concurrency and
   coroutines
   

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4. “Coroutines are computer program components that
   generalize subroutines for nonpreemptive multitasking, by
   allowing multiple entry points for suspending and resuming
   execution at certain locations” - Wikipedia
   "coroutines are functions whose execution you can
   pause"- Brett Cannon (Python core)
   -or-
   

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5. Isn’t that like threading?
   

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6. Common
   use cases
   ● Event driven applications
   ● IO bound applications
   ● Long running IO events
   (websockets)
   ● Applications which make lots
   of network requests
   (uploading/downloading data)
   

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7. Once upon a time...
   

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8. 1. Generators
   

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9. 1.1 yield
   (PEP 255, Python 2.2)
   

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10. 1.1 Generators - yield
    def eager_range(up_to):
    """Create a list of integers,
    from 0 to up_to, exclusive."""
    sequence = []
    index = 0
    while index < up_to:
    sequence.append(index)
    index += 1
    return sequence
    

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11. 1.1 Generators - yield
    def lazy_range(up_to):
    """Generator to return the
    sequence of integers from 0 to
    up_to, exclusive."""
    index = 0
    while index < up_to:
    yield index
    index += 1
    

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12. 1.2 value = yield
    (PEP 342, Python 2.5)
    

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13. 1.2 Generators - value = yield
    def jumping_range(up_to):
    """Generator for the sequence of integers from 0 to up_to, exclusive.
    Sending a value into the generator will shift the sequence by that amount.
    """
    index = 0
    while index < up_to:
    jump = yield index
    if jump is None:
    jump = 1
    index += jump
    if __name__ == '__main__':
    iterator = jumping_range(5)
    print(next(iterator)) # 0
    print(iterator.send(2)) # 2
    print(next(iterator)) # 3
    print(iterator.send(-1)) # 2
    for x in iterator:
    print(x) # 3, 4
    

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14. 1.3 yield from
    (PEP 380, Python 3.3)
    

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15. 1.3 Generators - yield from
    yield from iterator
    # was roughly equivalent to
    for x in iterator:
    yield x
    

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16. 1.3 Generators - yield from
    def bottom():
    # Returning the yield lets the value that goes up the call stack to come right back
    # down.
    return (yield 42)
    def middle():
    return (yield from bottom())
    def top():
    return (yield from middle())
    # Get the generator.
    gen = top()
    value = next(gen)
    print(value) # Prints '42'.
    

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17. 2. asyncio
    (Python 3.4)
    

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18. An event loop
    “is a programming construct that waits for and dispatches
    events or messages in a program” - Wikipedia
    

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19. 2.1 @asyncio.coroutine
    (Python 3.4)
    

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20. 2.1 asyncio - coroutine
    import time
    def countdown(number, n):
    while n > 0:
    print('T-minus', n, '({})'.format(number))
    time.sleep(1)
    n -= 1
    countdown("A", 2)
    countdown("B", 3)
    Output
    T-minus 2 (A)
    T-minus 1 (A)
    T-minus 3 (B)
    T-minus 2 (B)
    T-minus 1 (B)
    Time taken: 5s
    

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21. Demo
    2.1 asyncio - coroutine
    

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22. 2.1 asyncio - coroutine
    import asyncio
    @asyncio.coroutine
    def countdown(number, n):
    while n > 0:
    print('T-minus', n, '({})'.format(number))
    yield from asyncio.sleep(1)
    n -= 1
    loop = asyncio.get_event_loop()
    tasks = [
    asyncio.ensure_future(countdown("A", 2)),
    asyncio.ensure_future(countdown("B", 3))]
    loop.run_until_complete(asyncio.wait(tasks))
    loop.close()
    Output
    T-minus 2 (A)
    T-minus 3 (B)
    T-minus 1 (A)
    T-minus 2 (B)
    T-minus 1 (B)
    Time taken: 3s
    

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23. Demo
    2.1 asyncio - coroutine
    

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24. 2.2 Future and Task
    (Python 3.4)
    

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25. 4. aiohttp
    A Future is an object that represents the result of work that
    hasn’t completed.
    A Task is a wrapper for a coroutine and a subclass of
    Future.
    

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26. Job 1
    Job 2
    Job 1.1
    Job 2.1
    Job 1.1.1
    

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27. 3. async and await
    

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28. 3. async and await
    # Python 3.4
    @asyncio.coroutine
    def py34_coro():
    yield from stuff()
    # Python 3.5
    async def py35_coro():
    await stuff()
    

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29. 4. Compatible libraries
    

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30. 4.1 aiohttp
    (PEP 3156)
    HTTP client/server for asyncio
    

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31. 4.1 aiohttp
    ● Supports both Client and HTTP Server.
    ● Supports both Server WebSockets and Client
    WebSockets out-of-the-box.
    ● Web-server has Middlewares, Signals and pluggable
    routing.
    

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32. 4.1.1 Libraries - aiohttp - client
    import aiohttp
    import asyncio
    import async_timeout
    async def fetch(session, url):
    with async_timeout.timeout(10):
    async with session.get(url) as response:
    return await response.text()
    async def main():
    async with aiohttp.ClientSession() as session:
    html = await fetch(session, 'http://python.org')
    print(html)
    loop = asyncio.get_event_loop()
    loop.run_until_complete(main())
    

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33. Demo
    4.1.1 Libraries - aiohttp - client
    

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34. 4.1.2 Libraries - aiohttp - server
    from aiohttp import web
    async def handle(request):
    name = request.match_info.get('name', "Anonymous")
    text = "Hello, " + name
    return web.Response(text=text)
    app = web.Application()
    app.router.add_get('/', handle)
    app.router.add_get('/{name}', handle)
    web.run_app(app)
    

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35. 4.2 asynctest
    Unit tests for asyncio
    

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36. 4.3 database modules
    asyncpg, aiomysql, aioodbc,
    motor, asyncio-redis, aioes...
    

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37. 5. run_in_executor
    aka legacy support
    

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38. 5.1 run_in_executor - blocking
    import asyncio
    import time
    async def my_blocking_coroutine():
    print("Blocking started")
    time.sleep(4)
    print("Blocking done")
    async def my_nonblocking_coroutine():
    print("Nonblocking started")
    await asyncio.sleep(2)
    print("Nonblocking done")
    loop = asyncio.get_event_loop()
    tasks = [
    asyncio.ensure_future(my_nonblocking_coroutine()),
    asyncio.ensure_future(my_blocking_coroutine())]
    loop.run_until_complete(asyncio.wait(tasks))
    

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39. Demo
    5.1 run_in_executor - blocking
    

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40. 5.2 run_in_executor - nonblocking
    import asyncio
    import time
    async def my_blocking_coroutine():
    print("Blocking started")
    await loop.run_in_executor(None, time.sleep, 4)
    print("Blocking done")
    async def my_nonblocking_coroutine():
    print("Nonblocking started")
    await asyncio.sleep(2)
    print("Nonblocking done")
    loop = asyncio.get_event_loop()
    tasks = [
    asyncio.ensure_future(my_nonblocking_coroutine()),
    asyncio.ensure_future(my_blocking_coroutine())]
    loop.run_until_complete(asyncio.wait(tasks))
    

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41. Demo
    5.2 run_in_executor - blocking
    

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42. There’s even
    more!
    but we don’t have time for that
    (you may have even lost the will to live by now)
    ● Queues
    ● Gathers
    ● Sockets
    ● Signals
    ● Pipes
    ● Transports
    ● Streams
    ● Subprocesses
    ● Exceptions
    ● Protocols
    ● more...
    

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43. Further Reading
    http://www.snarky.ca/how-the-heck-does-async-await-work-in-python-3-5
    https://docs.python.org/3/library/asyncio.html
    http://lucumr.pocoo.org/2016/10/30/i-dont-understand-asyncio/
    https://carlosmaniero.github.io/asyncio-handle-blocking-functions.html
    https://github.com/dabeaz/curio
    

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