[Python-Dev] async __setitem__

Martin Teichmann lkb.teichmann at gmail.com
Fri Jun 19 14:56:51 CEST 2015

Hi everyone,

I was really happy to see PEP 492 - that is really a big step forward.
It makes many programming constructs possible in combination with
asyncio, which have been cumbersome or impossible until now.

One thing that still is impossible is to have __setitem__ be used
asynchronously. As an example, I am working with a database that
I access over the network, and it is easy to write

    data = await table[key]

to get something out of the database. But getting something in, I have
to write something like

    await table.set(key, value)

It would be cool if I could just write

    await table[key] = value

which would, I think, fit in nicely with all of PEP 492.

That said, I was hesitating which keyword to use, await or async. PEP 492
says something like async is an adjective, await a command. Then for
setitem, technically, I would need an adverb, so "asyncly table[key] = value".
But I didn't want to introduce yet another keyword (two different ones for the
same thing are already confusing enough), so I arbitrarily chose await.

If we are really going for it (I don't see the use case yet, I just
mention it for
completeness), we could also be extend this to other points where variables
are set, e.g. "for await i in something():" which is a bit similar to
"async for i in something()" yet different.



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