Re: Await expressions

Lawrence D'Oliveiro <ldo@nz.invalid> writes:

It can be a tricky thing to get to grips with, particularly if you are
trying to understand how it works at a low level.

  Does "await f()" (immediately) call "f()"?

  To find this out, I wrote the following program.

  I assume that the next function executed after executing
  "await sleep()" is "sleep" and encoded this in assertions.
  So far, this assumption never failed.

  So, directly after the eternal task executes "await sleep()",
  it is always the coroutine sleep() that starts, it never
  happens that the other task continues before this happens.

  Also, "caller" in "sleep" is "main", "eternal", or "other" as if
  "sleep" is called from one of those (as one would naïvely expect).

  So, it seems that "await f()" indeed will call f().

import asyncio as _asyncio
import inspect as _inspect
import random as _random

next = ''

async def sleep():
    global next
    assert next == 'sleep'
    next = ''
    caller = ''
    frameinfo = _inspect.stack( 1 )
    if frameinfo: caller = frameinfo[ 1 ].function
    await _asyncio.sleep( 0.0000000001 )

async def eternal():
    global next
    while True:
        assert next != 'sleep'
        next = 'sleep'
        await sleep()

async def other():
    global next
    while True:
        assert next != 'sleep'
        next = 'sleep'
        await sleep()

async def main():
    global next
    assert next != 'sleep'
    eternal_task = _asyncio.get_running_loop().create_task( eternal() )
    next = 'sleep'
    await sleep()
    other_task = _asyncio.get_running_loop().create_task( other() )
    await eternal_task

_asyncio.run( main() )