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Re: Stop writing Python 4 incompatible code

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From Chris Angelico <rosuav@gmail.com>
Newsgroups comp.lang.python
Subject Re: Stop writing Python 4 incompatible code
Date Thu, 14 Jan 2016 12:21:23 +1100
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On Thu, Jan 14, 2016 at 12:02 PM, BartC <bc@freeuk.com> wrote:
> I was surprised recently by just how much incompatibility there was between
> Python 2 and 3. It wasn't just about print with parentheses and range
> instead of xrange.
>
> I wanted to try out a jpeg decoder with PyPy and the three different ones I
> could find only worked with 2.x. Attempts to fix the incompatibilities
> usually lead to deeper mire.

This implies that there are many differences between 2.x and 3.x.

> In the end it was easier to put together my own version, which ran on all
> Pythons (2.7 to 3.4). It was surprisingly easy to do; no need for
> conditional version code.

But this implies that the differences are pretty simple. Which
argument are you putting?

The biggest difference between 2.x and 3.x is the handling of text vs
bytes. This is a very important distinction, but for a lot of
programs, it's not difficult; most of what you'll be using will be
text, and the only difference is that the 3.x version of your program
can handle all of Unicode. If you open any files, you might need to
specify encoding="utf-8" or encoding="ascii" or something, but that's
about the only issue.

> (It was also smaller and considerably faster than the others even before I
> went tried PyPy. Using range in 2.7 instead of xrange didn't make much
> difference either.)

Yeah, the effectiveness of xrange over range isn't significant on
smallish lists. And PyPy can optimize all sorts of things. If I'm
writing 2/3 compatible code, I'll usually just use range() everywhere,
unless I know for sure that the lists are going to be huge.

ChrisA

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Thread

Stop writing Python 4 incompatible code Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2016-01-13 18:30 +1100
  Re: Stop writing Python 4 incompatible code sjmsoft@gmail.com - 2016-01-13 06:21 -0800
    Re: Stop writing Python 4 incompatible code Random832 <random832@fastmail.com> - 2016-01-13 11:25 -0500
      Re: Stop writing Python 4 incompatible code Steven D'Aprano <steve@pearwood.info> - 2016-01-14 11:10 +1100
        Re: Stop writing Python 4 incompatible code Bernardo Sulzbach <mafagafogigante@gmail.com> - 2016-01-13 22:40 -0200
          Re: Stop writing Python 4 incompatible code Steven D'Aprano <steve@pearwood.info> - 2016-01-14 12:02 +1100
            Re: Stop writing Python 4 incompatible code Michael Torrie <torriem@gmail.com> - 2016-01-13 18:24 -0700
            Re: Stop writing Python 4 incompatible code Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2016-01-13 21:39 -0500
            Re: Stop writing Python 4 incompatible code Gene Heskett <gheskett@wdtv.com> - 2016-01-13 21:59 -0500
            Re: Stop writing Python 4 incompatible code Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2016-01-14 07:41 -0500
            Re: Stop writing Python 4 incompatible code Peter Otten <__peter__@web.de> - 2016-01-14 14:43 +0100
            Re: Stop writing Python 4 incompatible code "D'Arcy J.M. Cain" <darcy@VybeNetworks.com> - 2016-01-14 08:47 -0500
            Re: Stop writing Python 4 incompatible code Peter Otten <__peter__@web.de> - 2016-01-14 16:32 +0100
            Re: Stop writing Python 4 incompatible code "D'Arcy J.M. Cain" <darcy@VybeNetworks.com> - 2016-01-14 10:47 -0500
            Re: Stop writing Python 4 incompatible code Peter Otten <__peter__@web.de> - 2016-01-14 17:52 +0100
            Re: Stop writing Python 4 incompatible code Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2016-01-15 16:08 +1300
              Re: Stop writing Python 4 incompatible code Chris Angelico <rosuav@gmail.com> - 2016-01-15 15:56 +1100
                Re: Stop writing Python 4 incompatible code Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2016-01-16 10:02 +1300
              Re: Stop writing Python 4 incompatible code Bernardo Sulzbach <mafagafogigante@gmail.com> - 2016-01-15 09:40 -0200
          Re: Stop writing Python 4 incompatible code Robin Koch <robin.koch@t-online.de> - 2016-01-15 19:29 +0100
            Re: Stop writing Python 4 incompatible code Bernardo Sulzbach <mafagafogigante@gmail.com> - 2016-01-15 16:43 -0200
        Re: Stop writing Python 4 incompatible code Terry Reedy <tjreedy@udel.edu> - 2016-01-13 19:53 -0500
        Re: Stop writing Python 4 incompatible code Rick Johnson <rantingrickjohnson@gmail.com> - 2016-01-13 17:02 -0800
          Re: Stop writing Python 4 incompatible code Chris Angelico <rosuav@gmail.com> - 2016-01-14 12:29 +1100
          Re: Stop writing Python 4 incompatible code Michael Torrie <torriem@gmail.com> - 2016-01-13 19:11 -0700
            Re: Stop writing Python 4 incompatible code Rick Johnson <rantingrickjohnson@gmail.com> - 2016-01-13 18:51 -0800
              Re: Stop writing Python 4 incompatible code Chris Angelico <rosuav@gmail.com> - 2016-01-14 14:08 +1100
                Re: Stop writing Python 4 incompatible code Rick Johnson <rantingrickjohnson@gmail.com> - 2016-01-13 19:29 -0800
                Re: Stop writing Python 4 incompatible code Michael Torrie <torriem@gmail.com> - 2016-01-13 22:18 -0700
                Re: Stop writing Python 4 incompatible code Rick Johnson <rantingrickjohnson@gmail.com> - 2016-01-14 07:30 -0800
                Re: Stop writing Python 4 incompatible code Chris Angelico <rosuav@gmail.com> - 2016-01-15 04:41 +1100
                Re: Stop writing Python 4 incompatible code Rick Johnson <rantingrickjohnson@gmail.com> - 2016-01-14 10:40 -0800
                Re: Stop writing Python 4 incompatible code <paul.hermeneutic@gmail.com> - 2016-01-14 13:16 -0700
                Re: Stop writing Python 4 incompatible code Steven D'Aprano <steve@pearwood.info> - 2016-01-15 09:04 +1100
                Re: Stop writing Python 4 incompatible code Rick Johnson <rantingrickjohnson@gmail.com> - 2016-01-14 15:16 -0800
                Re: Stop writing Python 4 incompatible code Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2016-01-14 19:16 +1100
                Re: Stop writing Python 4 incompatible code wxjmfauth@gmail.com - 2016-01-14 01:37 -0800
          Re: Stop writing Python 4 incompatible code Terry Reedy <tjreedy@udel.edu> - 2016-01-14 00:45 -0500
            Re: Stop writing Python 4 incompatible code Rick Johnson <rantingrickjohnson@gmail.com> - 2016-01-14 07:52 -0800
              Re: Stop writing Python 4 incompatible code Ian Kelly <ian.g.kelly@gmail.com> - 2016-01-14 15:52 -0700
                Re: Stop writing Python 4 incompatible code Rick Johnson <rantingrickjohnson@gmail.com> - 2016-01-14 15:55 -0800
                Re: Stop writing Python 4 incompatible code Emile van Sebille <emile@fenx.com> - 2016-01-15 06:52 -0800
                Re: Stop writing Python 4 incompatible code Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2016-01-16 09:49 +1300
                Re: Stop writing Python 4 incompatible code Rick Johnson <rantingrickjohnson@gmail.com> - 2016-01-15 14:34 -0800
                Re: Stop writing Python 4 incompatible code Rick Johnson <rantingrickjohnson@gmail.com> - 2016-01-15 13:45 -0800
                Re: Stop writing Python 4 incompatible code William Ray Wing <wrw@mac.com> - 2016-01-15 12:02 -0500
                Re: Stop writing Python 4 incompatible code Bernardo Sulzbach <mafagafogigante@gmail.com> - 2016-01-15 16:09 -0200
                Re: Stop writing Python 4 incompatible code Alister <alister.ware@ntlworld.com> - 2016-01-15 18:46 +0000
                Re: Stop writing Python 4 incompatible code Bernardo Sulzbach <mafagafogigante@gmail.com> - 2016-01-15 16:55 -0200
                Re: Stop writing Python 4 incompatible code Alister <alister.ware@ntlworld.com> - 2016-01-16 14:41 +0000
                Re: Stop writing Python 4 incompatible code Bernardo Sulzbach <mafagafogigante@gmail.com> - 2016-01-16 12:48 -0200
                Re: Stop writing Python 4 incompatible code paul.hermeneutic@gmail.com - 2016-01-16 09:08 -0700
                Re: Stop writing Python 4 incompatible code William Ray Wing <wrw@mac.com> - 2016-01-16 13:00 -0500
                Re: Stop writing Python 4 incompatible code Michael Torrie <torriem@gmail.com> - 2016-01-16 12:26 -0700
                Re: Stop writing Python 4 incompatible code Chris Angelico <rosuav@gmail.com> - 2016-01-17 13:43 +1100
                Re: Stop writing Python 4 incompatible code William Ray Wing <wrw@mac.com> - 2016-01-15 13:49 -0500
                Re: Stop writing Python 4 incompatible code Bernardo Sulzbach <mafagafogigante@gmail.com> - 2016-01-15 16:53 -0200
                Re: Stop writing Python 4 incompatible code Mark Lawrence <breamoreboy@yahoo.co.uk> - 2016-01-15 20:58 +0000
                Re: Stop writing Python 4 incompatible code Christopher Reimer <christopher_reimer@icloud.com> - 2016-01-15 14:09 -0800
                Re: Stop writing Python 4 incompatible code Christopher Reimer <christopher_reimer@icloud.com> - 2016-01-16 20:51 -0800
    Re: Stop writing Python 4 incompatible code Chris Angelico <rosuav@gmail.com> - 2016-01-14 03:38 +1100
  Re: Stop writing Python 4 incompatible code Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2016-01-14 10:38 +1300
    Re: Stop writing Python 4 incompatible code Bernardo Sulzbach <mafagafogigante@gmail.com> - 2016-01-13 19:46 -0200
  Re: Stop writing Python 4 incompatible code BartC <bc@freeuk.com> - 2016-01-14 01:02 +0000
    Re: Stop writing Python 4 incompatible code Chris Angelico <rosuav@gmail.com> - 2016-01-14 12:21 +1100
      Re: Stop writing Python 4 incompatible code BartC <bc@freeuk.com> - 2016-01-14 01:49 +0000

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