Re: What is considered an "advanced" topic in Python?

From	Ben Bacarisse <ben.usenet@bsb.me.uk>
Newsgroups	comp.lang.python
Subject	Re: What is considered an "advanced" topic in Python?
Date	2015-06-01 14:22 +0100
Organization	A noiseless patient Spider
Message-ID	<87zj4j4l7a.fsf@bsb.me.uk> (permalink)
References	(5 earlier) <rosuav@gmail.com> <CAPTjJmpmM-jMszyMPSxch5CT4L43cMsXQbkyGGxvFXVpY2CdkA@mail.gmail.com> <201506010758.t517wR9T015894@fido.openend.se> <CAPTjJmrvi0EPyhV49hmqPxi1ztcZHmCn8hKzHhR7Y8_bkd7ZCw@mail.gmail.com> <mailman.278.1433154504.5151.python-list@python.org>

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Laura Creighton <lac@openend.se> writes:

> In a message of Mon, 01 Jun 2015 19:45:31 +1000, Chris Angelico writes:
>>On Mon, Jun 1, 2015 at 5:58 PM, Laura Creighton <lac@openend.se> wrote:
>>> If you are giving a talk about Decimal -- and trying to stamp out the
>>> inappropriate use of floats you have to first inform people that
>>> what they learned as 'decimals' as children was not floating point,
>>> despite the fact that we write them the same way.

That may be focusing on the wrong aspect because what you learn in
school (at least in the UK) is not so dissimilar to floating point
arithmetic.  The differences between that and machine floating point are
that (a) machines typically use base 2 (so the set of fractions that can
be represented exactly is a surprise); (b) machines use fixed-size
floating point whereas at school the representation, whilst always
finite, is more elastic; and (c) the base you calculate in is the base
you are given the data in and also the base you have to give the result
in.

For example, when a pupil is asked to "calculate 1.5 x 10^3 + 1.01 x
10^2 to two decimal places" what they will do is very similar to what a
machine would do if it had decimal floating point.  The surprises that
come from using typical machine floating point come from two base
conversions and (possibly) from rounding at every stage rather than just
at the end.

<snip>
> You have missed my point.  What I want is for floats never to be
> represented as '.' or ',' notation.  That way, when each naive
> user writes his or her first program that deals with money, when
> they look at their computer manual they will come to the section on
> floating point numbers and they will all look like something they
> have never seen before.

I agree that the key in to learn enough about what is going on.  Maybe
the solution is to teach people fixed-width binary floating point
arithmetic in schools!

> So they will read the section carefully
> to see if this is what they want or need, and the section can nicely
> say NEVER USE THIS FOR MONEY and they will know they are in the wrong
> place.

I know what you mean by this but it still bothers me a bit!  My first
job was writing programs for an economist.  It was all about money but,
being macro economics, was all in floating-point.  (In those days you
could not solve sets of non-linear differential equations in reasonable
time using anything else, but even if you could there would be no
point.)

Even some kinds of accounting can be done using floating point.  You can
use "scaled integers" in floating point to get some advantages over
integer arithmetic.  You might get a wider range (~53 bits rather than
32 say) and you get very simple checks for many overflow conditions.
You can also arrange for a simple check that you've failed to round
correctly at some step -- any non-integer fractional part will usually
indicate this.

I'm not averse to a blanket warning as the simplest way to get the
message across to beginners, but it's slowly becoming a "fact" that
nothing to do with money can be done correctly using floating point.

<snip>
-- 
Ben.

Thread

What is considered an "advanced" topic in Python? Mike Driscoll <kyosohma@gmail.com> - 2015-05-29 09:01 -0700
  Re: What is considered an "advanced" topic in Python? Joel Goldstick <joel.goldstick@gmail.com> - 2015-05-29 12:08 -0400
    Re: What is considered an "advanced" topic in Python? Mike Driscoll <kyosohma@gmail.com> - 2015-05-29 09:55 -0700
  Re: What is considered an "advanced" topic in Python? Chris Angelico <rosuav@gmail.com> - 2015-05-30 02:09 +1000
    Re: What is considered an "advanced" topic in Python? Mike Driscoll <kyosohma@gmail.com> - 2015-05-29 09:57 -0700
      Re: What is considered an "advanced" topic in Python? Chris Angelico <rosuav@gmail.com> - 2015-05-30 03:08 +1000
      Re: What is considered an "advanced" topic in Python? random832@fastmail.us - 2015-05-31 23:18 -0400
      Re: What is considered an "advanced" topic in Python? Chris Angelico <rosuav@gmail.com> - 2015-06-01 13:43 +1000
      Re: What is considered an "advanced" topic in Python? Laura Creighton <lac@openend.se> - 2015-06-01 09:58 +0200
        Re: What is considered an "advanced" topic in Python? Marko Rauhamaa <marko@pacujo.net> - 2015-06-01 12:36 +0300
          Zero [was Re: What is considered an "advanced" topic in Python?] Steven D'Aprano <steve@pearwood.info> - 2015-06-01 22:07 +1000
            Re: Zero [was Re: What is considered an "advanced" topic in Python?] Laura Creighton <lac@openend.se> - 2015-06-01 14:52 +0200
            Re: Zero [was Re: What is considered an "advanced" topic in Python?] Dave Farrance <DaveFarrance@OMiTTHiSyahooANDTHiS.co.uk> - 2015-06-01 13:56 +0100
              Re: Zero [was Re: What is considered an "advanced" topic in Python?] Skip Montanaro <skip.montanaro@gmail.com> - 2015-06-01 08:14 -0500
                Re: Zero [was Re: What is considered an "advanced" topic in Python?] Dave Farrance <df@see.replyto.invalid> - 2015-06-01 15:39 +0100
              Re: Zero [was Re: What is considered an "advanced" topic in Python?] Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-06-01 18:35 +0100
              Re: Zero [was Re: What is considered an "advanced" topic in Python?] Terry Reedy <tjreedy@udel.edu> - 2015-06-01 17:32 -0400
            Re: Zero [was Re: What is considered an "advanced" topic in Python?] Marko Rauhamaa <marko@pacujo.net> - 2015-06-01 16:18 +0300
              Re: Zero [was Re: What is considered an "advanced" topic in Python?] random832@fastmail.us - 2015-06-01 09:32 -0400
        Re: What is considered an "advanced" topic in Python? Dave Farrance <DaveFarrance@OMiTTHiSyahooANDTHiS.co.uk> - 2015-06-01 11:44 +0100
          Re: What is considered an "advanced" topic in Python? Marko Rauhamaa <marko@pacujo.net> - 2015-06-01 13:54 +0300
        Re: What is considered an "advanced" topic in Python? Rustom Mody <rustompmody@gmail.com> - 2015-06-01 22:33 -0700
      Re: What is considered an "advanced" topic in Python? Chris Angelico <rosuav@gmail.com> - 2015-06-01 19:45 +1000
      Re: What is considered an "advanced" topic in Python? Laura Creighton <lac@openend.se> - 2015-06-01 12:28 +0200
        Re: What is considered an "advanced" topic in Python? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-06-01 14:22 +0100
      Re: What is considered an "advanced" topic in Python? Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-06-01 11:34 +0100
      Re: What is considered an "advanced" topic in Python? Chris Angelico <rosuav@gmail.com> - 2015-06-01 20:36 +1000
      Re: What is considered an "advanced" topic in Python? Laura Creighton <lac@openend.se> - 2015-06-01 13:00 +0200
      Re: What is considered an "advanced" topic in Python? Laura Creighton <lac@openend.se> - 2015-06-01 13:24 +0200
        Re: What is considered an "advanced" topic in Python? Marko Rauhamaa <marko@pacujo.net> - 2015-06-01 14:57 +0300
          Re: What is considered an "advanced" topic in Python? BartC <bc@freeuk.com> - 2015-06-01 13:27 +0100
          Re: What is considered an "advanced" topic in Python? MRAB <python@mrabarnett.plus.com> - 2015-06-01 13:27 +0100
          Re: What is considered an "advanced" topic in Python? Laura Creighton <lac@openend.se> - 2015-06-01 17:07 +0200
            Re: What is considered an "advanced" topic in Python? alister <alister.nospam.ware@ntlworld.com> - 2015-06-01 15:26 +0000
              Re: What is considered an "advanced" topic in Python? Laura Creighton <lac@openend.se> - 2015-06-01 17:51 +0200
              Re: What is considered an "advanced" topic in Python? MRAB <python@mrabarnett.plus.com> - 2015-06-01 18:06 +0100
                Re: What is considered an "advanced" topic in Python? Marko Rauhamaa <marko@pacujo.net> - 2015-06-01 20:14 +0300
            Re: What is considered an "advanced" topic in Python? BartC <bc@freeuk.com> - 2015-06-01 16:42 +0100
              Re: What is considered an "advanced" topic in Python? Grant Edwards <invalid@invalid.invalid> - 2015-06-01 17:02 +0000
                Re: What is considered an "advanced" topic in Python? Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-06-01 18:45 +0100
                Re: What is considered an "advanced" topic in Python? Grant Edwards <invalid@invalid.invalid> - 2015-06-01 18:23 +0000
        Re: What is considered an "advanced" topic in Python? BartC <bc@freeuk.com> - 2015-06-01 13:24 +0100
      Re: What is considered an "advanced" topic in Python? Chris Angelico <rosuav@gmail.com> - 2015-06-01 23:52 +1000
        Re: What is considered an "advanced" topic in Python? BartC <bc@freeuk.com> - 2015-06-01 16:17 +0100
          Re: What is considered an "advanced" topic in Python? Chris Angelico <rosuav@gmail.com> - 2015-06-02 02:10 +1000
            Re: What is considered an "advanced" topic in Python? Rustom Mody <rustompmody@gmail.com> - 2015-06-01 21:46 -0700
  Re: What is considered an "advanced" topic in Python? Skip Montanaro <skip.montanaro@gmail.com> - 2015-05-29 11:39 -0500
    Re: What is considered an "advanced" topic in Python? Mike Driscoll <kyosohma@gmail.com> - 2015-05-29 09:58 -0700
  Re: What is considered an "advanced" topic in Python? Chris Angelico <rosuav@gmail.com> - 2015-05-30 02:50 +1000
  Re: What is considered an "advanced" topic in Python? Todd <toddrjen@gmail.com> - 2015-05-29 19:02 +0200
  Re: What is considered an "advanced" topic in Python? sohcahtoa82@gmail.com - 2015-05-29 10:03 -0700
    Re: What is considered an "advanced" topic in Python? Ethan Furman <ethan@stoneleaf.us> - 2015-05-29 10:17 -0700
      Re: What is considered an "advanced" topic in Python? sohcahtoa82@gmail.com - 2015-05-29 14:06 -0700
        Re: What is considered an "advanced" topic in Python? Jason Swails <jason.swails@gmail.com> - 2015-05-29 17:28 -0400
        Re: What is considered an "advanced" topic in Python? Ethan Furman <ethan@stoneleaf.us> - 2015-05-29 14:39 -0700
        Re: What is considered an "advanced" topic in Python? Ethan Furman <ethan@stoneleaf.us> - 2015-05-29 14:44 -0700
    Re: What is considered an "advanced" topic in Python? Marko Rauhamaa <marko@pacujo.net> - 2015-05-29 20:24 +0300
  Re: What is considered an "advanced" topic in Python? Todd <toddrjen@gmail.com> - 2015-05-29 19:03 +0200
  Re: What is considered an "advanced" topic in Python? Steven D'Aprano <steve@pearwood.info> - 2015-05-30 03:55 +1000
    Re: What is considered an "advanced" topic in Python? Mike Driscoll <kyosohma@gmail.com> - 2015-05-29 13:38 -0700
  Re: What is considered an "advanced" topic in Python? Sturla Molden <sturla.molden@gmail.com> - 2015-05-30 12:15 +0000
  Re: What is considered an "advanced" topic in Python? jonathon <jonathon.blake@gmail.com> - 2015-05-30 19:32 +0000
  Re: What is considered an "advanced" topic in Python? Chris Angelico <rosuav@gmail.com> - 2015-05-31 08:24 +1000
  Re: What is considered an "advanced" topic in Python? "C.D. Reimer" <chris@cdreimer.com> - 2015-05-30 18:28 -0700
  Re: What is considered an "advanced" topic in Python? Rustom Mody <rustompmody@gmail.com> - 2015-05-30 20:30 -0700
    Re: What is considered an "advanced" topic in Python? Chris Angelico <rosuav@gmail.com> - 2015-05-31 14:25 +1000
      Re: What is considered an "advanced" topic in Python? Rustom Mody <rustompmody@gmail.com> - 2015-05-30 21:46 -0700
        Re: What is considered an "advanced" topic in Python? Chris Angelico <rosuav@gmail.com> - 2015-05-31 14:58 +1000
          Re: What is considered an "advanced" topic in Python? Rustom Mody <rustompmody@gmail.com> - 2015-05-30 22:18 -0700
  Re: What is considered an "advanced" topic in Python? Gene Heskett <gheskett@wdtv.com> - 2015-06-01 09:49 -0400
  Re: What is considered an "advanced" topic in Python? Denis McMahon <denismfmcmahon@gmail.com> - 2015-06-01 15:30 +0000
  Re: What is considered an "advanced" topic in Python? Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2015-06-01 20:33 -0400
  Re: What is considered an "advanced" topic in Python? Gene Heskett <gheskett@wdtv.com> - 2015-06-01 23:30 -0400

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