Event Loop Internals — Series 2

Preview — 3 of 10 questions

What is the output of the following code?

javascript

import asyncio

async def worker():
    await asyncio.sleep(0.01)

async def main():
    task = asyncio.create_task(worker())
    coro = task.get_coro()
    print(coro is not None)
    print(asyncio.iscoroutine(coro))
    await task

asyncio.run(main())

ATrue, False — the coroutine returned by get_coro() is a distinct copy, not recognized as a real coroutine object.

BTrue, True

CAttributeError: 'Task' object has no attribute 'get_coro'

DFalse, False — a Task doesn't retain a reference to its original coroutine once it starts running.

What is the output of the following code?

javascript

import asyncio

async def worker():
    try:
        await asyncio.sleep(10)
    except ValueError as e:
        print("caught:", e)
        return "recovered"

async def main():
    coro = worker()
    coro.send(None)
    try:
        result = coro.throw(ValueError("injected"))
    except StopIteration as e:
        print("result:", e.value)

asyncio.run(main())

Acaught: injected, then RuntimeError: coroutine raised StopIteration

BNothing is caught — the injected ValueError propagates straight out of .throw() uncaught.

Ccaught: injected, then result: None — the coroutine's return value isn't captured by StopIteration.value when triggered via .throw().

Dcaught: injected, then result: recovered

What is the output of the following code?

javascript

import asyncio

async def main():
    loop = asyncio.get_running_loop()
    log = []
    loop.call_soon(lambda: log.append("first"))
    loop.call_soon(lambda: log.append("second"))
    loop.call_soon(lambda: log.append("third"))
    await asyncio.sleep(0.01)
    print(log)

asyncio.run(main())

A['first', 'second', 'third']

B['third', 'second', 'first'] — call_soon schedules callbacks onto a stack, so the most recently scheduled one runs first.

CUnpredictable order, since call_soon doesn't guarantee any particular scheduling order.

DTypeError: call_soon() missing required argument

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