Re: functions, optional parameters

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Date	Sun, 10 May 2015 13:33:00 +1000
Subject	Re: functions, optional parameters
From	Chris Angelico <rosuav@gmail.com>
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On Sun, May 10, 2015 at 12:45 PM, Steven D'Aprano
<steve+comp.lang.python@pearwood.info> wrote:
> This is the point where some people try to suggest some sort of complicated,
> fragile, DWIM heuristic where the compiler tries to guess whether the user
> actually wants the default to use early or late binding, based on what the
> expression looks like. "0 is an immutable int, use early binding; [] is a
> mutable list, use late binding." sort of thing. Such a thing might work
> well for the obvious cases, but it would be a bugger to debug and
> work-around for the non-obvious cases when it guesses wrong -- and it will.

What you could have is "late-binding semantics, optional early binding
as an optimization but only in cases where the result is
indistinguishable". That would allow common cases (int/bool/str/None
literals) to be optimized, since there's absolutely no way for them to
evaluate differently.

I personally don't think it'd be that good an idea, but it's a simple
enough rule that it wouldn't break anything. As far as anyone's code
is concerned, the rule is "late binding, always". In fact, that would
be the language definition; the rest is an optimization. (It's like
how "x.y()" technically first looks up attribute "y" on object x, then
calls the result; but it's perfectly reasonable for a Python
implementation to notice this extremely common case and do an
"optimized method call" that doesn't actually create a function
object.) The simpler the rule, the easier to grok, and therefore the
less chance of introducing bugs.

ChrisA

Thread

functions, optional parameters Michael Welle <mwe012008@gmx.net> - 2015-05-08 13:59 +0200
  Re: functions, optional parameters Rustom Mody <rustompmody@gmail.com> - 2015-05-08 05:09 -0700
    Re: functions, optional parameters Michael Welle <mwe012008@gmx.net> - 2015-05-08 14:36 +0200
  Re: functions, optional parameters Chris Angelico <rosuav@gmail.com> - 2015-05-08 22:39 +1000
    Re: functions, optional parameters Michael Welle <mwe012008@gmx.net> - 2015-05-08 14:57 +0200
  Re: functions, optional parameters Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-05-09 01:24 +1000
    Re: functions, optional parameters Chris Angelico <rosuav@gmail.com> - 2015-05-09 02:02 +1000
      Re: functions, optional parameters Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-05-09 03:36 +1000
        Re: functions, optional parameters Chris Angelico <rosuav@gmail.com> - 2015-05-09 03:49 +1000
          Re: functions, optional parameters Mel Wilson <mwilson@the-wire.com> - 2015-05-08 18:49 +0000
          Re: functions, optional parameters Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2015-05-09 13:41 +1200
            Re: functions, optional parameters Chris Angelico <rosuav@gmail.com> - 2015-05-09 12:05 +1000
              Re: functions, optional parameters Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2015-05-09 19:27 +1200
          Re: functions, optional parameters Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-05-09 12:52 +1000
    Re: functions, optional parameters Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-05-09 03:26 +1000
    Re: functions, optional parameters Michael Welle <mwe012008@gmx.net> - 2015-05-08 17:50 +0200
      Re: functions, optional parameters Ian Kelly <ian.g.kelly@gmail.com> - 2015-05-09 10:57 -0600
      Re: functions, optional parameters Chris Angelico <rosuav@gmail.com> - 2015-05-10 13:33 +1000
        Re: functions, optional parameters Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-05-10 15:20 +1000
          Re: functions, optional parameters Chris Angelico <rosuav@gmail.com> - 2015-05-10 18:59 +1000
      Re: functions, optional parameters Rustom Mody <rustompmody@gmail.com> - 2015-05-09 20:35 -0700
        Re: functions, optional parameters Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-05-10 15:25 +1000
      Re: functions, optional parameters Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-05-10 12:45 +1000
        Re: functions, optional parameters Dave Angel <davea@davea.name> - 2015-05-10 07:25 -0400
        Re: functions, optional parameters Chris Angelico <rosuav@gmail.com> - 2015-05-11 00:39 +1000
        Re: functions, optional parameters Michael Welle <mwe012008@gmx.net> - 2015-05-11 07:58 +0200
    Re: functions, optional parameters Ian Kelly <ian.g.kelly@gmail.com> - 2015-05-08 09:48 -0600

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