Asynchronous Python

A short introduction to asynchronous programming and asyncio, which was introduced in Python 3.4.

Transcript

1. ASYNCHRONOUS PYTHON
2. WHY ASYNC?
3. SYNCHRONOUS MODEL Credit: http://krondo.com/?p=1209
4. SYNCHRONOUS MODEL Credit: http://krondo.com/?p=1209
5. THREADED MODEL Credit: http://krondo.com/?p=1209
6. ASYNCHRONOUS MODEL Credit: http://krondo.com/?p=1209
7. WHY ASYNC? • Synchronous model ◦ CPU idles too much • Threaded model ◦ Difficult to code (locks, thread coordination) ◦ Context switching ◦ Idling problem is still there
8. UNDER THE SURFACE select, poll etc (Unix) IOCP (Windows, Solaris)
9. CALLBACK vs. COROUTINE
10. CALLBACKS Twisted, Tornado JavaScript
11. CALLBACK HELL
12. “ It requires superhuman discipline to write readable code in callbacks and if you don’t believe me look at any piece of JavaScript code. - Guido van Rossum Source: https://www.youtube.com/watch?v=1coLC-MUCJc
13. COROUTINES • Write async code like it was sync • Make use of yield • Before Python 3.4 we have gevent
14. asyncio codenamed “tulip” But now in Python 3.4 we have
15. HELLO WORLD (Callback Style) import asyncio def hello_world(loop): print('Hello World') loop.stop() loop = asyncio.get_event_loop() # Schedule a call to hello_world() loop.call_soon(hello_world, loop) # Blocking call interrupted by loop.stop() loop.run_forever() loop.close()
16. HELLO WORLD (Coroutine Style) import asyncio @asyncio.coroutine def hello_world(): print("Hello World!") loop = asyncio.get_event_loop() # Blocking call which returns when the hello_world() # coroutine is done loop.run_until_complete(hello_world()) loop.close()
17. EXAMPLE: STOCK VALUATION WITH GLASSDOOR RATING
18. P/E ratio = Price / Earnings per share Low P/E ➭ the stock is cheap
19. P/E ratio = Price / Earnings per share Low P/E ➭ the stock is cheap PEG = PE ratio / Glassdoor rating
20. def get_PE(symbol): # Scrape Google Finance and return the PE ratio def get_glassdoor_rating(symbol): # Scrape Glassdoor and return the rating of the company def compute_PEG(symbol): return get_PE(symbol) / get_glassdoor_rating(symbol) # Main program for symbol in [‘AAPL’, ‘FB’, ‘GOOGL’]: print(compute_PEG(symbol)) SYNC IMPLEMENTATION
21. def compute_PEG(symbol): return get_PE(symbol) / get_glassdoor_rating(symbol) class PegThread(Thread): def __init__(self, symbol): self.symbol = symbol def run(self): print(compute_PEG(self.symbol)) # Main program for symbol in [‘AAPL’, ‘FB’, ‘GOOGL’]: PegThread(symbol).start() THREADED IMPLEMENTATION
22. @asyncio.coroutine def compute_PEG(symbol): pe = yield from get_PE(symbol) g = yield from get_glassdoor_rating(symbol) return pe / g @asyncio.coroutine def print_PEG(symbol): peg = yield from compute_PEG(symbol) print(peg) # Main program loop = asyncio.get_event_loop() tasks = [print_PEG(symbol) for symbol in [‘AAPL’, ‘FB’, ‘GOOGL’]] loop.run_until_complete(asyncio.wait(tasks)) ASYNC IMPLEMENTATION
23. yield from f() is equivalent to for x in f(): yield x
24. @asyncio.coroutine def compute_PEG(symbol): pe, g = yield from asyncio.gather(get_PE(symbol), get_glassdoor_rating(symbol)) return pe / g @asyncio.coroutine def print_PEG(symbol): peg = yield from compute_PEG(symbol) print(peg) # Main program loop = asyncio.get_event_loop() tasks = [print_PEG(symbol) for symbol in [‘AAPL’, ‘FB’, ‘GOOGL’]] loop.run_until_complete(asyncio.wait(tasks)) ASYNC IMPLEMENTATION II
25. DEMO http://github.com/eliangcs/asyncio-demo
26. asyncio IS READY!
27. “aio” FAMILY aiohttp aiohttp.web aiopg aioredis aiomysql aioes ...
28. SUMMARY
29. Synchronous programming sucks
30. Threaded programming sucks
31. Callback-style async programming sucks
32. Coroutine-style async programming ROCKS!
33. asyncio IS THE FUTURE