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Re: extend methods of decimal module

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On Fri, Feb 28, 2014 at 6:34 PM, Steven D'Aprano <steve@pearwood.info> wrote:
> On Fri, 28 Feb 2014 16:00:10 +1100, Chris Angelico wrote:
>
>> If we had some other tag, like 'd', we could actually construct a
>> Decimal straight from the source code. Since source code is a string,
>> it'll be constructed from that string, and it'll never go via float.
>
> Now that Python has a fast C implementation of Decimal, I would be happy
> for Python 4000 to default to decimal floats, and require special syntax
> for binary floats. Say, 0.1b if you want a binary float, and 0.1 for a
> decimal.

Maybe, but I believe the cdecimal module is still slower than typical
floating point. There'd also be considerations regarding NumPy and how
you'd go about working with an array of non-integer values, and so on.
Certainly this will be an extremely reasonable topic of discussion
once there's any notion of a Py4K on the cards. There'll be arguments
on both sides.

> But for now, backwards-compatibility requires that the default floating
> point type remains binary float. But we could maybe agitate for a 1.234d
> Decimal literal type. Care to write a PEP?
>
> :-)

Heh. Strong consideration here: it would mean importing the decimal
module on startup.

>>> t=time.time(); import decimal; time.time()-t
4.5000159740448
>>> t=time.time(); import decimal; time.time()-t
0.0

A dummy import (when it's already loaded) is so fast that it's
immeasurable, but four and a half seconds to load up decimal? This is
3.4.0b2 on Windows, btw. It was a lot quicker on my Linux box,
probably because the OS or disk cache had the file. So maybe it
wouldn't be too bad in practice; but it's still a cost to consider.

>> The question is how far Python wants to bless the Decimal type with
>> syntax - after all, if Decimal can get a literal notation, why can't
>> Fraction, and why can't all sorts of other types? And that's a huge can
>> of worms.
>
> I like Fractions, but I don't think they're important enough for the
> average users to require literal notation.

Yeah, but where do you draw the line? Either decimal.Decimal becomes a
built-in type, or there needs to be a system for constructing literals
of non-built-in types. And if Decimal becomes built-in, then why that
and not <<insert type name here>>?

Also, if Decimal becomes a built-in type, does that affect the numeric tower?

ChrisA

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extend methods of decimal module "Mark H. Harris" <harrismh777@gmail.com> - 2014-02-19 07:30 -0800
  Re: extend methods of decimal module Terry Reedy <tjreedy@udel.edu> - 2014-02-19 13:59 -0500
    Re: extend methods of decimal module "Mark H. Harris" <harrismh777@gmail.com> - 2014-02-19 13:30 -0800
      Re: extend methods of decimal module Zachary Ware <zachary.ware+pylist@gmail.com> - 2014-02-19 15:54 -0600
      Re: extend methods of decimal module Terry Reedy <tjreedy@udel.edu> - 2014-02-19 17:10 -0500
        Re: extend methods of decimal module "Mark H. Harris" <harrismh777@gmail.com> - 2014-02-27 04:07 -0800
          Re: extend methods of decimal module Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2014-02-27 14:42 +0000
            Re: extend methods of decimal module "Mark H. Harris" <harrismh777@gmail.com> - 2014-02-27 07:42 -0800
              Re: extend methods of decimal module Chris Angelico <rosuav@gmail.com> - 2014-02-28 02:57 +1100
              Re: extend methods of decimal module Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2014-02-27 16:24 +0000
                Re: extend methods of decimal module "Mark H. Harris" <harrismh777@gmail.com> - 2014-02-27 15:00 -0800
                Re: extend methods of decimal module Wolfgang <xpysol@gmail.com> - 2014-02-27 15:43 -0800
                Re: extend methods of decimal module Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2014-02-27 23:50 +0000
                Re: extend methods of decimal module "Mark H. Harris" <harrismh777@gmail.com> - 2014-02-27 18:15 -0800
                Re: extend methods of decimal module Chris Angelico <rosuav@gmail.com> - 2014-02-28 15:26 +1100
                Re: extend methods of decimal module "Mark H. Harris" <harrismh777@gmail.com> - 2014-02-27 21:18 -0800
                Re: extend methods of decimal module Chris Angelico <rosuav@gmail.com> - 2014-02-28 16:26 +1100
                Re: extend methods of decimal module Wolfgang Maier <wolfgang.maier@biologie.uni-freiburg.de> - 2014-02-28 08:54 +0000
                Re: extend methods of decimal module "Mark H. Harris" <harrismh777@gmail.com> - 2014-02-28 10:23 -0800
                Re: extend methods of decimal module Steven D'Aprano <steve@pearwood.info> - 2014-02-28 03:15 +0000
                Re: extend methods of decimal module "Mark H. Harris" <harrismh777@gmail.com> - 2014-02-27 20:41 -0800
                Re: extend methods of decimal module Chris Angelico <rosuav@gmail.com> - 2014-02-28 16:00 +1100
                Re: extend methods of decimal module Steven D'Aprano <steve@pearwood.info> - 2014-02-28 07:34 +0000
                Re: extend methods of decimal module Chris Angelico <rosuav@gmail.com> - 2014-02-28 19:52 +1100
                Re: extend methods of decimal module Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-02-28 15:11 +0000
                Re: extend methods of decimal module Chris Angelico <rosuav@gmail.com> - 2014-03-01 02:36 +1100
                Re: extend methods of decimal module "Mark H. Harris" <harrismh777@gmail.com> - 2014-02-28 10:34 -0800
                Re: extend methods of decimal module Chris Angelico <rosuav@gmail.com> - 2014-03-01 05:37 +1100
                Re: extend methods of decimal module "Mark H. Harris" <harrismh777@gmail.com> - 2014-02-28 11:26 -0800
                Re: extend methods of decimal module "Mark H. Harris" <harrismh777@gmail.com> - 2014-02-28 11:39 -0800
                Re: extend methods of decimal module "Mark H. Harris" <harrismh777@gmail.com> - 2014-02-28 12:17 -0800
          Re: extend methods of decimal module Terry Reedy <tjreedy@udel.edu> - 2014-02-27 12:07 -0500
            Re: extend methods of decimal module Anssi Saari <as@sci.fi> - 2014-03-01 08:55 +0200
              Re: extend methods of decimal module "Mark H. Harris" <harrismh777@gmail.com> - 2014-03-01 16:49 -0800
          Re: extend methods of decimal module Chris Angelico <rosuav@gmail.com> - 2014-02-28 04:48 +1100
      Re: extend methods of decimal module Zachary Ware <zachary.ware+pylist@gmail.com> - 2014-02-19 16:27 -0600
      Re: extend methods of decimal module casevh@gmail.com - 2014-02-19 21:11 -0800
        Re: extend methods of decimal module "Mark H. Harris" <harrismh777@gmail.com> - 2014-02-27 02:33 -0800
          Re: extend methods of decimal module casevh@gmail.com - 2014-02-28 06:23 -0800
  Re: extend methods of decimal module Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2014-02-19 22:29 +0000
    Re: extend methods of decimal module "Mark H. Harris" <harrismh777@gmail.com> - 2014-02-27 02:37 -0800

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