Re: Encapsulation in Python

From	Chris Angelico <rosuav@gmail.com>
Newsgroups	comp.lang.python
Subject	Re: Encapsulation in Python
Date	2016-03-15 12:23 +1100
Message-ID	<mailman.148.1458005017.12893.python-list@python.org> (permalink)
References	(12 earlier) <nc7ef9$sgf$1@dont-email.me> <mailman.137.1457997645.12893.python-list@python.org> <nc7it9$ejq$1@dont-email.me> <mailman.140.1458001784.12893.python-list@python.org> <nc7n8k$qru$1@dont-email.me>

Show all headers | View raw

On Tue, Mar 15, 2016 at 12:10 PM, BartC <bc@freeuk.com> wrote:
> The one-byte-code switch works when all case expressions are known at
> compile-time. It makes use of a jump-table within the byte-code.
>
> The total sequence will be more than one byte-code, typically:
>
> LOAD_FAST                The index
> SWITCH                   Jump to the right label
> ....
> L5:                      One of multiple labels
>  ...                     Deal with the code in this branch
> JUMP_ABSOLUTE            Break out of the switch
>
> ...                      Provision is needed for the jump-table
>
> But only one is needed for testing and dispatch. Now I've sketched it out,
> perhaps you can fill in the details for yourself... (I'm not getting
> involved in CPython development.)

Let's be fair here; anyone can make a single byte-code that does
arbitrary amounts of work. (Consider Python's CALL_FUNCTION or the old
PRINT_ITEM opcode.) How much work does SWITCH do here? Does the jump
table require that the possible case values be compact? If they're
not, how does it operate?

In Python, the most obvious way to do the repeated comparisons would
be a hash lookup. The SWITCH opcode could take a dictionary that maps
values to jump targets, with an 'else' target if the lookup fails, and
jump to that. It would actually be possible to implement this entirely
in an optimizer, with code written like this:

if x == 'asdf':
    ...
elif x == 'qwer':
    ...
elif x in ('zxcv', '1234'):
    ...
else:
    ...

Or, of course, it could get its own syntax.

ChrisA

Thread

Re: Encapsulation in Python Ian Kelly <ian.g.kelly@gmail.com> - 2016-03-10 08:27 -0700
  Re: Encapsulation in Python Rick Johnson <rantingrickjohnson@gmail.com> - 2016-03-10 16:45 -0800
    Re: Encapsulation in Python Ian Kelly <ian.g.kelly@gmail.com> - 2016-03-11 08:47 -0700
      Re: Encapsulation in Python Rick Johnson <rantingrickjohnson@gmail.com> - 2016-03-11 18:39 -0800
        Re: Encapsulation in Python Ian Kelly <ian.g.kelly@gmail.com> - 2016-03-12 09:44 -0700
          Re: Encapsulation in Python Rick Johnson <rantingrickjohnson@gmail.com> - 2016-03-12 19:11 -0800
          Re: Encapsulation in Python Steven D'Aprano <steve@pearwood.info> - 2016-03-13 21:11 +1100
            Re: Encapsulation in Python Rick Johnson <rantingrickjohnson@gmail.com> - 2016-03-14 10:32 -0700
              Re: Encapsulation in Python Ian Kelly <ian.g.kelly@gmail.com> - 2016-03-14 15:09 -0600
              Re: Encapsulation in Python Mark Lawrence <breamoreboy@yahoo.co.uk> - 2016-03-14 21:23 +0000
                Re: Encapsulation in Python BartC <bc@freeuk.com> - 2016-03-14 22:07 +0000
                Re: Encapsulation in Python Mark Lawrence <breamoreboy@yahoo.co.uk> - 2016-03-14 22:20 +0000
                Re: Encapsulation in Python BartC <bc@freeuk.com> - 2016-03-14 22:40 +0000
                Re: Encapsulation in Python Mark Lawrence <breamoreboy@yahoo.co.uk> - 2016-03-14 23:19 +0000
                Re: Encapsulation in Python BartC <bc@freeuk.com> - 2016-03-14 23:56 +0000
                Re: Encapsulation in Python Chris Angelico <rosuav@gmail.com> - 2016-03-15 11:12 +1100
                Re: Encapsulation in Python BartC <bc@freeuk.com> - 2016-03-15 00:54 +0000
                Re: Encapsulation in Python Chris Angelico <rosuav@gmail.com> - 2016-03-15 11:58 +1100
                Re: Encapsulation in Python BartC <bc@freeuk.com> - 2016-03-15 01:22 +0000
                Re: Encapsulation in Python Chris Angelico <rosuav@gmail.com> - 2016-03-15 13:02 +1100
                Re: Encapsulation in Python Mark Lawrence <breamoreboy@yahoo.co.uk> - 2016-03-15 00:28 +0000
                Re: Encapsulation in Python BartC <bc@freeuk.com> - 2016-03-15 01:10 +0000
                Re: Encapsulation in Python Chris Angelico <rosuav@gmail.com> - 2016-03-15 12:23 +1100
                Re: Encapsulation in Python Mark Lawrence <breamoreboy@yahoo.co.uk> - 2016-03-15 04:41 +0000
                Re: Encapsulation in Python rurpy@yahoo.com - 2016-03-14 17:17 -0700
                Re: Encapsulation in Python Chris Angelico <rosuav@gmail.com> - 2016-03-15 11:25 +1100
                Re: Encapsulation in Python Steven D'Aprano <steve@pearwood.info> - 2016-03-15 13:06 +1100
                Re: Encapsulation in Python Chris Angelico <rosuav@gmail.com> - 2016-03-15 13:14 +1100
                Re: Encapsulation in Python Steven D'Aprano <steve@pearwood.info> - 2016-03-15 13:40 +1100
                Re: Encapsulation in Python Rick Johnson <rantingrickjohnson@gmail.com> - 2016-03-14 21:08 -0700
                Re: Encapsulation in Python Mark Lawrence <breamoreboy@yahoo.co.uk> - 2016-03-15 00:47 +0000
                Re: Encapsulation in Python Steven D'Aprano <steve@pearwood.info> - 2016-03-15 13:46 +1100
                Re: Encapsulation in Python Chris Angelico <rosuav@gmail.com> - 2016-03-15 11:56 +1100
                Re: Encapsulation in Python Mark Lawrence <breamoreboy@yahoo.co.uk> - 2016-03-15 04:36 +0000
                Re: Encapsulation in Python Steven D'Aprano <steve@pearwood.info> - 2016-03-15 13:01 +1100
                Re: Encapsulation in Python Mark Lawrence <breamoreboy@yahoo.co.uk> - 2016-03-15 04:45 +0000
                Re: Encapsulation in Python Christian Gollwitzer <auriocus@gmx.de> - 2016-03-15 22:02 +0100
                Re: Encapsulation in Python BartC <bc@freeuk.com> - 2016-03-16 00:39 +0000
                Re: Encapsulation in Python BartC <bc@freeuk.com> - 2016-03-16 22:58 +0000
        Re: Encapsulation in Python sohcahtoa82@gmail.com - 2016-03-14 11:11 -0700
          Re: Encapsulation in Python Rick Johnson <rantingrickjohnson@gmail.com> - 2016-03-14 23:09 -0700
      Re: Encapsulation in Python Rick Johnson <rantingrickjohnson@gmail.com> - 2016-03-11 18:56 -0800
    Re: Encapsulation in Python Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2016-03-12 13:52 +1300
      Re: Encapsulation in Python Rick Johnson <rantingrickjohnson@gmail.com> - 2016-03-12 08:49 -0800
        Re: Encapsulation in Python Chris Angelico <rosuav@gmail.com> - 2016-03-13 08:10 +1100
          Re: Encapsulation in Python Rick Johnson <rantingrickjohnson@gmail.com> - 2016-03-12 19:36 -0800
            Re: Encapsulation in Python Chris Angelico <rosuav@gmail.com> - 2016-03-13 15:05 +1100
        Re: Encapsulation in Python Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2016-03-14 12:35 +1300
          Re: Encapsulation in Python Rick Johnson <rantingrickjohnson@gmail.com> - 2016-03-14 15:55 -0700

csiph-web