afar 0.2.1

Run code on a dask worker via a context manager

Afar

One man's magic is another man's engineering
Robert A. Heinlein

---

afar allows you to run code on a remote Dask worker using context managers. For example:

import afar

with afar.run, remotely:
    import dask_cudf
    df = dask_cudf.read_parquet("s3://...")
    result = df.sum().compute()

Outside the context, result is a Dask Future whose data resides on a worker. result.result() is necessary to copy the data locally.

By default, only the last assignment is saved. One can specify which variables to save:

with afar.run("one", "two"), remotely:
    one = 1
    two = one + 1

one and two are now both Futures. They can be used directly in other afar.run contexts:

with afar.run as data, remotely:
    three = one + two

assert three.result() == 3
assert data["three"].result() == 3

data above is a dictionary of variable names to Futures. It may be necessary at times to get the data from here. Alternatively, you may pass a mapping to afar.run to use as the data.

run = afar.run(data={"four": 4})
with run, remotely:
    seven = three + four
assert run.data["seven"].result() == 7

If you want to automatically gather the data locally (to avoid calling .result()), use afar.get instead of afar.run:

with afar.get, remotely:
    five = two + three
assert five == 5

Is this a good idea?

I don't know!

For motivation, see https://github.com/dask/distributed/issues/4003

It's natural to be skeptical of unconventional syntax. Often times, I don't think it's obvious whether new syntax will be nice to use, and you really just need to try it out and see.

We're still exploring the usability of afar. If you try it out, please share what you think, and ask yourself questions such as:

• can we spell anything better?
• does this offer opportunities?
• what is surprising?
• what is lacking?

Here's an example of an opportunity:

on_gpus = afar.remotely(resources={"GPU": 1})

with afar.run, on_gpus:
    ...

This now works! Keyword arguments to remotely will be passed to client.submit.

I don't know about you, but I think this is starting to look and feel kinda nice, and it could probably be even better :)

This code is highly experimental and magical!