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Re: Why Python 3?

References (3 earlier) <CALwzidmk9ogErqsF9ghM4_Bi=+n2qwCTpqJ48exOgg+L-2Gd_Q@mail.gmail.com> <CAPTjJmqcr+ZhtRRxGtOVX6ppLd=1RyQ2yU9X=fFy4zH8oLrHyA@mail.gmail.com> <CALwzid=HrxL7kCwM5LOKEgwQT+YzrCH0xV57LXEjqU6jtsti=g@mail.gmail.com> <CAPTjJmrRm7hwb3pn8cj3_5qUKXj5urA2PK4raH2V_dtPWCacUg@mail.gmail.com> <CALwzidnRcrQA9qc=qJpROR106F2EJFr7KzLN9XeyyNXfJW-GSA@mail.gmail.com>
Date 2014-04-20 06:53 +1000
Subject Re: Why Python 3?
From Chris Angelico <rosuav@gmail.com>
Newsgroups comp.lang.python
Message-ID <mailman.9372.1397940783.18130.python-list@python.org> (permalink)

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On Sun, Apr 20, 2014 at 6:38 AM, Ian Kelly <ian.g.kelly@gmail.com> wrote:
>> Or you just cast one of them to float. That way you're sure you're
>> working with floats.
>
> Which is inappropriate if the type passed in was a Decimal or a complex.

In that case, you already have a special case in your code, so whether
that special case is handled by the language or by your code makes
little difference. Is your function so generic that it has to be able
to handle float, Decimal, or complex, and not care about the
difference, and yet has to ensure that int divided by int doesn't
yield int? Then say so; put in that special check. Personally, I've
yet to meet any non-toy example of a function that needs that exact
handling; most code doesn't ever think about complex numbers, and a
lot of things look for one specific type:

>>> "asdf"*3.0
Traceback (most recent call last):
  File "<pyshell#19>", line 1, in <module>
    "asdf"*3.0
TypeError: can't multiply sequence by non-int of type 'float'

Maybe it's not your code that should be caring about what happens when
you divide two integers, but the calling code. If you're asking for
the average of a list of numbers, and they're all integers, and the
avg() function truncates to integer, then the solution is to use sum()
and explicitly cast to floating point before dividing. Why should the
language handle that? It's no different from trying to sum a bunch of
different numeric types:

>>> sum([1.0,decimal.Decimal("1")])
Traceback (most recent call last):
  File "<pyshell#25>", line 1, in <module>
    sum([1.0,decimal.Decimal("1")])
TypeError: unsupported operand type(s) for +: 'float' and 'decimal.Decimal'

The language doesn't specify a means of resolving the conflict between
float and Decimal, but for some reason the division of two integers is
blessed with a language feature. Again, it would make perfect sense if
float were a perfect superset of int, so that you could simply declare
that 1.0 and 1 behave absolutely identically in all arithmetic (they
already hash and compare equally), but that's not the case, so I don't
see that division should try to pretend they are.

ChrisA

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Thread

Why Python 3? Anthony Papillion <papillion@gmail.com> - 2014-04-18 22:28 -0500
  Re: Why Python 3? Paul Rubin <no.email@nospam.invalid> - 2014-04-18 23:40 -0700
    Re: Why Python 3? Chris Angelico <rosuav@gmail.com> - 2014-04-19 17:34 +1000
      Re: Why Python 3? Roy Smith <roy@panix.com> - 2014-04-19 09:26 -0400
        Re: Why Python 3? Chris Angelico <rosuav@gmail.com> - 2014-04-19 23:42 +1000
        Re: Why Python 3? Albert-Jan Roskam <fomcl@yahoo.com> - 2014-04-19 10:57 -0700
        Re: Why Python 3? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-04-20 10:07 +0000
    Re: Why Python 3? Ian Kelly <ian.g.kelly@gmail.com> - 2014-04-19 03:25 -0600
      Re: Why Python 3? Marko Rauhamaa <marko@pacujo.net> - 2014-04-19 12:59 +0300
    Re: Why Python 3? Chris Angelico <rosuav@gmail.com> - 2014-04-19 19:37 +1000
      Integer and float division [was Re: Why Python 3?] Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-04-20 11:02 +0000
        Re: Integer and float division [was Re: Why Python 3?] Jussi Piitulainen <jpiitula@ling.helsinki.fi> - 2014-04-20 15:38 +0300
          Re: Integer and float division [was Re: Why Python 3?] Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-04-20 15:09 +0000
        Re: Integer and float division [was Re: Why Python 3?] Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2014-04-21 11:44 +1200
    Re: Why Python 3? Terry Reedy <tjreedy@udel.edu> - 2014-04-19 13:23 -0400
      Re: Why Python 3? Paul Rubin <no.email@nospam.invalid> - 2014-04-19 20:25 -0700
        Re: Why Python 3? Ben Finney <ben+python@benfinney.id.au> - 2014-04-20 19:15 +1000
        Re: Why Python 3? Walter Hurry <walterhurry@lavabit.com> - 2014-04-20 23:50 +0000
          Re: Why Python 3? Chris Angelico <rosuav@gmail.com> - 2014-04-21 10:00 +1000
            Re: Why Python 3? HoneyMonster <nobody@someplace.invalid> - 2014-04-21 04:08 +0000
          Re: Why Python 3? Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-04-21 01:11 +0100
    Re: Why Python 3? Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-04-19 18:31 +0100
    Re: Why Python 3? Chris Angelico <rosuav@gmail.com> - 2014-04-20 03:53 +1000
    Re: Why Python 3? Ian Kelly <ian.g.kelly@gmail.com> - 2014-04-19 13:58 -0600
    Re: Why Python 3? Chris Angelico <rosuav@gmail.com> - 2014-04-20 06:31 +1000
      Re: Why Python 3? Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2014-04-20 13:06 +1200
        Re: Why Python 3? Chris Angelico <rosuav@gmail.com> - 2014-04-20 11:28 +1000
          Re: Why Python 3? Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2014-04-21 10:52 +1200
            Re: Why Python 3? Chris Angelico <rosuav@gmail.com> - 2014-04-21 09:24 +1000
              Re: Why Python 3? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-04-21 03:43 +0000
                Re: Why Python 3? Chris Angelico <rosuav@gmail.com> - 2014-04-21 14:43 +1000
                Re: Why Python 3? Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2014-04-22 09:58 +1200
                Re: Why Python 3? Chris Angelico <rosuav@gmail.com> - 2014-04-21 14:48 +1000
                Re: Why Python 3? wxjmfauth@gmail.com - 2014-04-21 02:42 -0700
                Re: Why Python 3? Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2014-04-22 10:28 +1200
                Re: Why Python 3? Chris Angelico <rosuav@gmail.com> - 2014-04-22 08:43 +1000
                Re: Why Python 3? Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2014-04-22 18:03 +1200
        Re: Why Python 3? Terry Reedy <tjreedy@udel.edu> - 2014-04-20 00:17 -0400
          Re: Why Python 3? Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2014-04-21 11:13 +1200
            Re: Why Python 3? Terry Reedy <tjreedy@udel.edu> - 2014-04-20 20:09 -0400
    Re: Why Python 3? Ian Kelly <ian.g.kelly@gmail.com> - 2014-04-19 14:38 -0600
    Re: Why Python 3? Chris Angelico <rosuav@gmail.com> - 2014-04-20 06:53 +1000
      Re: Why Python 3? Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2014-04-20 13:35 +1200
    Re: Why Python 3? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-04-20 09:59 +0000
      Unicode in Python Rustom Mody <rustompmody@gmail.com> - 2014-04-21 20:57 -0700
        Re: Unicode in Python Terry Reedy <tjreedy@udel.edu> - 2014-04-22 01:44 -0400
          Re: Unicode in Python Rustom Mody <rustompmody@gmail.com> - 2014-04-21 23:18 -0700
            Re: Unicode in Python Chris Angelico <rosuav@gmail.com> - 2014-04-22 16:32 +1000
        Re: Unicode in Python Steven D'Aprano <steve@pearwood.info> - 2014-04-22 06:11 +0000
          Re: Unicode in Python Rustom Mody <rustompmody@gmail.com> - 2014-04-21 23:30 -0700
            Re: Unicode in Python Chris Angelico <rosuav@gmail.com> - 2014-04-22 16:44 +1000
            Re: Unicode in Python wxjmfauth@gmail.com - 2014-04-22 02:07 -0700
              Re: Unicode in Python Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-04-22 12:21 +0000
                Re: Unicode in Python wxjmfauth@gmail.com - 2014-04-22 08:28 -0700
        Re: Unicode in Python Ian Kelly <ian.g.kelly@gmail.com> - 2014-04-22 00:31 -0600
          Re: Unicode in Python Rustom Mody <rustompmody@gmail.com> - 2014-04-22 02:23 -0700
          Re: Unicode in Python Rustom Mody <rustompmody@gmail.com> - 2014-04-22 11:09 -0700
    Re: Why Python 3? Ian Kelly <ian.g.kelly@gmail.com> - 2014-04-20 10:22 -0600
      Re: Why Python 3? Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2014-04-21 11:56 +1200
        Re: Why Python 3? Ian Kelly <ian.g.kelly@gmail.com> - 2014-04-20 18:29 -0600
    Re: Why Python 3? MRAB <python@mrabarnett.plus.com> - 2014-04-20 17:41 +0100
    Re: Why Python 3? Chris Angelico <rosuav@gmail.com> - 2014-04-21 02:46 +1000
      Re: Why Python 3? Roy Smith <roy@panix.com> - 2014-04-20 14:40 -0700
        Re: Why Python 3? Terry Reedy <tjreedy@udel.edu> - 2014-04-20 17:58 -0400
        Re: Why Python 3? Richard Damon <Richard@Damon-Family.org> - 2014-04-20 18:02 -0400
          Re: Why Python 3? Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2014-04-21 12:22 +1200
        Re: Why Python 3? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-04-21 02:13 +0000
  Re: Why Python 3? Steve Hayes <hayesstw@telkomsa.net> - 2014-04-19 13:53 +0200
    Re: Why Python 3? Chris Angelico <rosuav@gmail.com> - 2014-04-19 22:46 +1000
    Re: Why Python 3? Rustom Mody <rustompmody@gmail.com> - 2014-04-19 08:59 -0700
  Re: Why Python 3? Rick Johnson <rantingrickjohnson@gmail.com> - 2014-04-19 07:41 -0700
  Re: Why Python 3? Thomas Lehmann <thomas.lehmann.private@googlemail.com> - 2014-05-06 09:28 -0700

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