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Date: Tue, 24 Feb 2015 13:03:06 +1100
Subject: Re: Future of Pypy?
From: Chris Angelico <rosuav@gmail.com>
Cc: "python-list@python.org" <python-list@python.org>
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On Tue, Feb 24, 2015 at 12:50 PM, Paul Rubin <no.email@nospam.invalid> wrote:
> Chris Angelico <rosuav@gmail.com> writes:
>>> What if you want to dynamically construct a callable and send it to
>>> another process?
>> I'm not sure what that would actually mean. Do you try to construct it
>> out of code that already exists in the other process? Are you passing
>> actual code to the other process?
>
> I gave an example in a reply to Steven, something like
>
>   other_thread_queue.put(lambda x: x*x)
>
> to tell the other thread it is supposed to square something.  It
> receives a callable and calls it in its own context.

So, you would have to pass code to the other process, probably. What about this:

y = 4
other_thread_queue.put(lambda x: x*y)

Or this:

y = [4]
def next_y():
    y[0] += 1
    return y[0]
other_thread_queue.put(next_y)

It may not be obvious with your squaring example, but every Python
function has its context (module globals, etc). You can't pass a
function around without also passing, or sharing, its data.

With threads in a single process, this isn't a problem. They all
access the same memory space, so they can all share state. As soon as
you go to separate processes, these considerations become serious.

ChrisA