Asynchronous programming

[Steven D'Aprano]

On Thu, 11 Aug 2016 03:06 pm, Paul Rubin wrote:

> The basic characteristic of asynchronous programming is that it involves
> changing all your usual blocking i/o calls to non-blocking ones, so your
> program can keep running as soon as your request is started.

That's the bit that confuses me. I understand about parallel processing, but
that's not what this is about.

Say I want to download data from a network, and it will take a long time. If
I can do the read in parallel to something else, that makes sense:

  begin downloading in another thread/process
  make a coffee
  process download


But what's the point in doing it asynchronously if I have to just wait for
it to complete?

  begin downloading in an async thread
  twiddle thumbs, doing nothing
  process download

Take Chris' "yield from" example, rewritten for await:


def asynchronous(id):
    trn = await conn.begin_transaction()
    await trn.execute("select name from people where id=%d", (id,))
    name, = await trn.fetchone()
    await trn.execute("update people set last_seen=now() where id=%d",(id,))
    await trn.commit()
    return name

Since I'm spending all my time waiting for the other things to return
control, why don't I just write it synchronously?

def synchronous(id):
    trn = conn.begin_transaction()
    trn.execute("select name from people where id=%d", (id,))
    name, = trn.fetchone()
    trn.execute("update people set last_seen=now() where id=%d", (id,))
    trn.commit()
    return name



-- 
Steve
“Cheer up,” they said, “things could be worse.” So I cheered up, and sure
enough, things got worse.