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Why Python 3?

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  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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#70420

On 2014-04-20 17:22, Ian Kelly wrote:
>
> On Apr 19, 2014 2:54 PM, "Chris Angelico" <rosuav@gmail.com
> <mailto:rosuav@gmail.com>> wrote:
>  >
>  > On Sun, Apr 20, 2014 at 6:38 AM, Ian Kelly <ian.g.kelly@gmail.com
> <mailto: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:
>
> When I'm writing a generic average function, I probably don't know
> whether it will ever be used to average complex numbers. That shouldn't
> matter, because I should be able to rely on this code working for
> whatever numeric type I pass in:
>
> def average(values):
>      return sum(values) / len(values)
>
> This works for decimals, it works for fractions, it works for complex
> numbers, it works for numpy types, and in Python 3 it works for ints.
>
>  > 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.
>
> First, that's not equivalent.  Try the following in Python 3:
>
> values = [int(sys.float_info.max / 10)] * 20
> print(average(values))
>
> Now try this:
>
> print(average(map(float, values)))
>
> I don't have an interpreter handy to test, but I expect the former to
> produce the correct result and the latter to raise OverflowError on the
> call to sum.
>

Python 3.4.0 (v3.4.0:04f714765c13, Mar 16 2014, 19:25:23) [MSC v.1600 64 
bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
 >>> import sys
 >>> def average(values):
...     return sum(values) / len(values)
...
 >>> values = [int(sys.float_info.max / 10)] * 20
 >>> print(average(values))
1.7976931348623158e+307
 >>> print(average(map(float, values)))
Traceback (most recent call last):
   File "<stdin>", line 1, in <module>
   File "<stdin>", line 2, in average
TypeError: object of type 'map' has no len()
 >>> print(average(list(map(float, values))))
inf
 >>>

In fact, that's true back to Python 3.1

> Second, why should the calling code have to worry about this
> implementation detail anyway? The point of a generic function is that
> it's generic.
>

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#70422

On Mon, Apr 21, 2014 at 2:22 AM, Ian Kelly <ian.g.kelly@gmail.com> wrote:
> When I'm writing a generic average function, I probably don't know whether
> it will ever be used to average complex numbers.

This keeps coming up in these discussions. How often do you really
write a function that generic? And if you do, isn't it doing something
so simple that it's then the caller's responsibility (not the
function's, and not the language's) to ensure that it gets the right
result?

ChrisA

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#70432

In article <mailman.9383.1398012417.18130.python-list@python.org>,
 Chris Angelico <rosuav@gmail.com> wrote:

> On Mon, Apr 21, 2014 at 2:22 AM, Ian Kelly <ian.g.kelly@gmail.com> wrote:
> > When I'm writing a generic average function, I probably don't know whether
> > it will ever be used to average complex numbers.
> 
> This keeps coming up in these discussions. How often do you really
> write a function that generic? And if you do, isn't it doing something
> so simple that it's then the caller's responsibility (not the
> function's, and not the language's) to ensure that it gets the right
> result?
> 
> ChrisA

Hmmm.  Taking the average of a set of complex numbers has a reasonable 
physical meaning.  But, once you start down that path, I'm not sure how 
far you can go before things no long make sense.  What's the standard 
deviation of a set of complex numbers?  Does that even have any meaning?

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#70433

On 4/20/2014 5:40 PM, Roy Smith wrote:
> In article <mailman.9383.1398012417.18130.python-list@python.org>,
>   Chris Angelico <rosuav@gmail.com> wrote:
>
>> On Mon, Apr 21, 2014 at 2:22 AM, Ian Kelly <ian.g.kelly@gmail.com> wrote:
>>> When I'm writing a generic average function, I probably don't know whether
>>> it will ever be used to average complex numbers.
>>
>> This keeps coming up in these discussions. How often do you really
>> write a function that generic? And if you do, isn't it doing something
>> so simple that it's then the caller's responsibility (not the
>> function's, and not the language's) to ensure that it gets the right
>> result?
>>
>> ChrisA
>
> Hmmm.  Taking the average of a set of complex numbers has a reasonable
> physical meaning.  But, once you start down that path, I'm not sure how
> far you can go before things no long make sense.  What's the standard
> deviation of a set of complex numbers?  Does that even have any meaning?

One can either calculate variance from the sum of squared distances from 
the mean point, or calculate x and y deviations separately and calculate 
the covariance matrix thereof.

-- 
Terry Jan Reedy

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#70434

On 4/20/14, 5:40 PM, Roy Smith wrote:
> In article <mailman.9383.1398012417.18130.python-list@python.org>,
>  Chris Angelico <rosuav@gmail.com> wrote:
> 
>> On Mon, Apr 21, 2014 at 2:22 AM, Ian Kelly <ian.g.kelly@gmail.com> wrote:
>>> When I'm writing a generic average function, I probably don't know whether
>>> it will ever be used to average complex numbers.
>>
>> This keeps coming up in these discussions. How often do you really
>> write a function that generic? And if you do, isn't it doing something
>> so simple that it's then the caller's responsibility (not the
>> function's, and not the language's) to ensure that it gets the right
>> result?
>>
>> ChrisA
> 
> Hmmm.  Taking the average of a set of complex numbers has a reasonable 
> physical meaning.  But, once you start down that path, I'm not sure how 
> far you can go before things no long make sense.  What's the standard 
> deviation of a set of complex numbers?  Does that even have any meaning?
> 

If you thing of the Standard Deviation being the Root Mean Norm2 of the
deviations, it has a very similar meaning as to over the reals, a
measure of the "spread" of the values.

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#70447

Richard Damon wrote:
> If you thing of the Standard Deviation being the Root Mean Norm2 of the
> deviations, it has a very similar meaning as to over the reals, a
> measure of the "spread" of the values.

NumPy appears to handle this:

http://docs.scipy.org/doc/numpy/reference/generated/numpy.std.html

See the comment on that page about complex numbers.

So yes, it is meaningful and apparently people use it.

-- 
Greg

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#70449

On Sun, 20 Apr 2014 14:40:38 -0700, Roy Smith wrote:

> In article <mailman.9383.1398012417.18130.python-list@python.org>,
>  Chris Angelico <rosuav@gmail.com> wrote:
> 
>> On Mon, Apr 21, 2014 at 2:22 AM, Ian Kelly <ian.g.kelly@gmail.com>
>> wrote:
>> > When I'm writing a generic average function, I probably don't know
>> > whether it will ever be used to average complex numbers.
>> 
>> This keeps coming up in these discussions. How often do you really
>> write a function that generic? And if you do, isn't it doing something
>> so simple that it's then the caller's responsibility (not the
>> function's, and not the language's) to ensure that it gets the right
>> result?
>> 
>> ChrisA
> 
> Hmmm.  Taking the average of a set of complex numbers has a reasonable
> physical meaning.  But, once you start down that path, I'm not sure how
> far you can go before things no long make sense.  What's the standard
> deviation of a set of complex numbers?  Does that even have any meaning?

Yes it does. Stdev is a measure of scale of the distribution, and is 
always real and non-negative. For complex values, you can calculate it 
using:

    (abs(x - mean))**2

which is how numpy does it, or from the complex conjugate:

    x1 = x-mean
    x1.conj()*x1


which is how Matlab does it.

http://docs.scipy.org/doc/numpy/reference/generated/numpy.std.html
http://www.mathworks.com.au/matlabcentral/newsreader/view_thread/57323


Hence the variance is always non-negative, and the standard deviation is 
always real. See also: 

https://en.wikipedia.org/wiki/Variance#Generalizations




-- 
Steven D'Aprano
http://import-that.dreamwidth.org/

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#70378

On Fri, 18 Apr 2014 22:28:05 -0500, Anthony Papillion <papillion@gmail.com>
wrote:

>Hello Everyone,
>
>So I've been working with Python for a while and I'm starting to take
>on more and more serious projects with it. I've been reading a lot
>about Python 2 vs Python 3 and the community kind of seems split on
>which should be used.
>
>Some say 'Python 3 is the future, use it for everything now' and other
>say 'Python 3 is the future but you can't do everything in it now so
>use Python 2'.

Yes, that made me more or less abandon my attempt to learn Python.

I had Python 3 on my computer (came on one of those freebie discs you get with
magazines, I think) and my son had a book on it, so I thought with the program
and the instructions I should be able to learn something. 

It took me a week, with some help from this forum, to get the Print statement
to work. 


-- 
Steve Hayes from Tshwane, South Africa
Web:  http://www.khanya.org.za/stevesig.htm
Blog: http://khanya.wordpress.com
E-mail - see web page, or parse: shayes at dunelm full stop org full stop uk

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#70380

On Sat, Apr 19, 2014 at 9:53 PM, Steve Hayes <hayesstw@telkomsa.net> wrote:
>>Some say 'Python 3 is the future, use it for everything now' and other
>>say 'Python 3 is the future but you can't do everything in it now so
>>use Python 2'.
>
> Yes, that made me more or less abandon my attempt to learn Python.
>
> I had Python 3 on my computer (came on one of those freebie discs you get with
> magazines, I think) and my son had a book on it, so I thought with the program
> and the instructions I should be able to learn something.
>
> It took me a week, with some help from this forum, to get the Print statement
> to work.

If your book and your interpreter didn't match, then that's a problem,
just as if you were working with different versions of any other
software. (Can you imagine reading through a Microsoft Excel tutorial
and trying to do the exercises in a different version of Excel?) The
print statement wouldn't work because there isn't one; the print
*function* will work quite happily, though. All you need is for
someone to explain it to you as a function, and you'll be fine.

ChrisA

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#70390

On Saturday, April 19, 2014 5:23:01 PM UTC+5:30, Steve Hayes wrote:
> It took me a week, with some help from this forum, to get the Print statement
> to work. 

How long does it take one to learn to drive a car?
To play the piano? To become a brain surgeon?

No I am not exactly in the "gung-ho over python 3" camp
However if you dont start out learning programming with an estimate of work somewhere between learning to:
- drive-a-car
- play-the-piano
you are setting yourself up for failure.
But its equally unreasonable to expect to learn programming more easy than to drive a car.

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#70387

On Friday, April 18, 2014 10:28:05 PM UTC-5, Anthony Papillion wrote:
> Hello Everyone,
> So I've been working with Python for a while and I'm starting to take
> on more and more serious projects with it. I've been reading a lot
> about Python 2 vs Python 3 and the community kind of seems split on
> which should be used.
> Some say 'Python 3 is the future, use it for everything now' and other
> say 'Python 3 is the future but you can't do everything in it now so
> use Python 2'.
> What is the general feel of /this/ community? I'm about to start a
> large scale Python project. Should it be done in 2 or 3? What are the
> benefits, aside from the 'it's the future' argument?

Python 3000 is the direct result of a hubris that even
surpasses Hitler's boneheaded attempt to fight the war on two
fronts. Yes, most of us agree that the changes are "positive
evolution" HOWEVER, are these minor repairs REALLY worth
polarizing a vibrant community and causing Python's
propagation to stagnate?

    HELL NO!

Who would want to choose Python for a scripting language for
their project when EVEN the community cannot agree on which
version is best to use? But even *IF* every respected member
was a total "high-knee smooching tool" of GvR parroting off
that "Python 3000 is the best!", we cannot ignore the
functionality concerns that will result from choosing
between 2x or 3x.

    NOBODY IS ACTIVELY CHOOSING PYTHON ANYMORE FOLKS!

Python is destined to destroy itself internally JUST like
the American society is currently destroying itself, and
what a travesty, since Python was the shining light of what
a program should be.

    THE REVOLUTION WILL NOT BE TELEVISED!

Python is set to become extinct because GvR bought his time
machine AFTER infecting the code base with a print
statement -- thanks Guido, thanks for everything! Maybe next
time you should consider buying bean stalk beans instead!

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#70976

Hi,

I can't give you the advise for a concrete version anyway there are lot of arguments given by the other posters. BUT there is a way how you can circumvent the problem to some extend:

Are you intending to use Jenkins? I don't want to convince you here why to use Jenkins but maybe I don't need to and THEN you just install the ShiningPanda plugin and each time your project is build automatically because of a change all tests are running across multiple Python versions. This way you won't have too many problems to switch to another newer Python version. Keep the build "green".


> 
> What is the general feel of /this/ community? I'm about to start a
> 
> large scale Python project. Should it be done in 2 or 3? What are the
> 
> benefits, aside from the 'it's the future' argument?

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