How async and await ended up in Python

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How async and await ended up in Python EuroPython 2018, Edinburgh

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Hello (: https:/ /www.hacksoft.io Django React Twitter: @pgergov_

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Python is synchronous

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Request Response

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Threads

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Asynchronous

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asyncio

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hello_asyncio.py import asyncio async def hello_world_coroutine(delay): print('Hello') await asyncio.sleep(delay) print(f'World, with delay: {delay}') loop = asyncio.get_event_loop() loop.create_task(hello_world_coroutine(1)) loop.create_task(hello_world_coroutine(2)) loop.run_forever()

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Python 3.6.3 Hell Hello World, with delay 1 World, with delay 2

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Coroutines are computer-program components that generalize subroutines for non-preemptive multitasking, by allowing multiple entry points for suspending and resuming execution at certain locations Wikipedia

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How async and await ended up in python Order of execution - raise and return Iterable and Iterator Generator functions - yield and .send Python 3.3 yield from Definition for coroutine in Python Python 3.4, @asyncio.coroutine Python 3.5, @types.coroutine async and await

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Order of execution

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throw_exception.py def throw_exception(): print('Will raise an Exception') raise Exception('Raised inside `throw_exception`') print('This message won\'t be printed')

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hello_world.py def hello_world(): print('Hello world!') return 42 print('This message will never be printed')

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yield

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Iterable __iter__ for x in iterable:

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Iterator __next__ __iter__

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class MyIterator: def __init__(self): self.counter = 1 def __iter__(self): return self def __next__(self): counter = self.counter if counter > 3: raise StopIteration self.counter += 1 return counter iterator.py

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iterator = MyIterator() next(iterator) # returns 1 next(iterator) # returns 2 next(iterator) # returns 3 next(iterator) # raises StopIteration 

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iterator = MyIterator() for numb in iterator: print(numb) 1 2 3

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Generator function

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def generator_function(): print('Going to yield first value') yield 1 print('Yielding second value') yield 2 generator_function.py

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gen = generator_function() next(gen) ‘Going to yield first value’ 1 next(gen) ‘Yielding second value’ 2 next(gen) # raises StopIteration 

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.send

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def generator_send(): print('Going to yield a value') received = yield 42 print(f'Received {received}') generator_send.py

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gen = generator_function() gen.send(None) ‘Going to yield value’ 42 gen.send(‘Hello generator’) ‘Received Hello generator’ StopIteration is raised

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yield from for x in iterator: yield x yield from iterator Python 3.3

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def first_generator(): yield 1 print('In the middle of first generator') yield 2 def second_generator(): gen = first_generator() yield from gen print('In the middle of second generator') yield 3 yield_from.py

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gen = second_generator() next(gen) 1 next(gen) In the middle of first generator 2 next(gen) In the middle of second generator 3 next(gen) # raises StopIteration

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definition of coroutine in Python Python 3.3

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@asyncio.coroutine Python 3.4

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Python 3.6.3 import asyncio async def hello_world_coroutine(delay): print('Hello') await asyncio.sleep(delay) print(f'World, with delay: {delay}') loop = asyncio.get_event_loop() loop.create_task(hello_world_coroutine(1)) loop.create_task(hello_world_coroutine(2)) loop.run_forever()

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Python 3.4 import asyncio @asyncio.coroutine def hello_world_coroutine(delay): print('Hello') yield from asyncio.sleep(delay) print(f'World, with delay: {delay}') loop = asyncio.get_event_loop() loop.create_task(hello_world_coroutine(1)) loop.create_task(hello_world_coroutine(2)) loop.run_forever()