AsyncIO - Generator Based (Python < 3.5)

Async generator-based coroutines have been introduced with PEP 3156 in Python 3.3 and are usable with the introduction of the asyncio library in Python 3.4. They already got replaced in Python 3.5. Support for generator-based coroutines in asyncio is deprecated and is removed in Python 3.11.

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()

Source

import asyncio

@asyncio.coroutine
def compute(x, y):
    print("Compute %s + %s ..." % (x, y))
    yield from asyncio.sleep(1.0) # uses a Future
    return x + y

@asyncio.coroutine
def print_sum(x, y):
    result = yield from compute(x, y)
    print("%s + %s = %s" % (x, y, result))

loop = asyncio.get_event_loop()
loop.run_until_complete(print_sum(1, 2))
loop.close()

The “Task” is created by the BaseEventLoop.run_until_complete() method when it gets a coroutine object instead of a task.

Source

Looks very familiar to our implementation isn’t it?

Summary

• Generator based coroutines are used for pre-emptive multitasking.

• asyncio provides an event loop.

• The loop is returned by a factory function.

• A main coroutine is run in the loop until it is finished.

• A Task is created for running the main coroutine.

• yield from is used to suspend and resume coroutines.

• Coroutines are marked as coroutines with a decorator.

• The coroutine decorator converts normal functions into coroutines.