[Tutor] What exactly does "await" do? (David)

[Alphonsus Okoye]

> ---------- Forwarded message ----------
> From: David <bouncingcats at gmail.com>
> To: tutor at python.org
> Cc:
> Bcc:
> Date: Tue, 14 Feb 2023 00:05:32 +1100
> Subject: Re: [Tutor] What exactly does "await" do?
> On Mon, 13 Feb 2023 at 21:41, Alphonsus Okoye <phonokoye at gmail.com> wrote:
>
> > How does the await
> > statement suspend the execution of a coroutine and still run the
coroutine?
> > I know I am missing some fundamentals here. How do I make sense of this?
>
> Let's choose one of the coroutines you posted, as an example to discuss.
> This one:
>
> > >    async def say_after(delay, what):
> > >        await asyncio.sleep(delay)
> > >        print(what)
>
> When execution reaches the 'await' statement in that coroutine,
> it suspends the execution of the running coroutine named 'say_after',
> and instead runs the coroutine named 'asyncio.sleep'.
>
> That's how 'await' both suspends a coroutine (the one it is in) and runs
> a coroutine (a different one that it starts).
>
> When the coroutine named 'asyncio.sleep' returns, the coroutine
> named 'say_after' will resume, from the 'print(what)' statement.
>
> A coroutine can be recognised by having 'async def' in its
> definition statement, as opposed to just 'def' for the
> definition of an ordinary function or method.


Good day Mr David and to everyone here. From what you said, the coroutine
can be executed just like a function; the execution of the main function is
suspended till the inner function has finished executing. What is then the
main purpose of a coroutine?

I assume there is a specific problem which isn't straightforward with
normal functions. From youtube videos, the purpose of a coroutine seems to
be to execute some IO process asynchronously, but I have also read in some
stackoverflow page that a coroutine may still not execute asynchronously if
not written well. So how do I write asynchronous code using coroutines?

More specifically, if I wished to write a program that read from a long
text file "spam.txt", and while the process begins to waste time, do other
stuff like call function doOtherStuff(), what would the code look like?