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Stop writing Python 4 incompatible code

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  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

Page 1 of 4  [1] 2 3 4  Next page →

#101592 — Stop writing Python 4 incompatible code

Quote:

    With the end of support for Python 2 on the horizon (in 2020),
    many package developers have made their packages compatible
    with both Python 2 and Python 3 by using constructs such as:

        if sys.version_info[0] == 2:
            # Python 2 code
        else:
            # Python 3 code

    [...]
    Another example of problematic code is the following:

        if six.PY2:
            # Python 2 code
        elif six.PY3:
            # Python 3 code

    In this case, no code will get executed on Python 4 at all!


[end quote]


http://astrofrog.github.io/blog/2016/01/12/stop-writing-python-4-
incompatible-code/

or http://tinyurl.com/jskt54s


Better still, don't do version checks *at all*. There is almost never any 
need for a version check. Better is to use feature detection:


try:
    xrange  # Succeeds in Python 2.
except NameError:
    xrange = range


Not only is this almost entirely future-proof[1] and avoids overly-specific 
version tests, but if your code happens to find itself running in a 
customized environment which has already monkey-patched builtins to re-add 
xrange, the first lookup will succeed and no extra work need be done.

You can be extremely fine-grained too:

try:
    casefold = str.casefold  # Succeeds in Python 3.3 or better
else:
    casefold = str.lower  # Poor Man's case-folding.
    # Or if you prefer:
    def casefold(s):
        ...


About the only thing I use version checking for is to decide which prompt I 
want to use:

if sys.version_info[0] >= 3 and os.name == 'posix':
    # Make the main prompt bold in Python 3. This probably won't
    # work on Windows, put it should(?) work on any POSIX system.
    sys.ps1 = '\001\x1b[1m\002py> \001\x1b[0m\002'
else:
    sys.ps1 = 'py> '


In Python 3, that highlights the prompt py> in bold.

You can detect the return type:

if isinstance(map(len, []), list):
    print("Python 2 version of map")
else:
    # Python 3, or Python 2 with future_builtins.
    print("Python 3 version of map")



and even the number and kind of arguments:

try:
    sorted([], cmp=None)
except TypeError:
    print("use key not cmp in Python 3")
    _sorted = sorted
    def sorted(L, cmp=None):
        if cmp is None:
            return _sorted(L)
        return _sorted(L, key=functools.cmp_to_key(cmp))



So remember, use feature detection, not version checking.






[1] It might fail if some distant version of Python adds an xrange which 
does something completely unexpected, or if it removes range; but surely 
nobody can be expected to write forward-compatible code in the face of 
changes of that magnitude.


-- 
Steve

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#101618

This strikes me as very good advice.  Thanks for being so far-sighted. And let's hope that Python 4 has fewer incompatibilities (none would good) than Python 3!

Cheers,
  Steve J. Martin

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#101628

On Wed, Jan 13, 2016, at 09:21, sjmsoft@gmail.com wrote:
> This strikes me as very good advice.  Thanks for being so far-sighted.
> And let's hope that Python 4 has fewer incompatibilities (none would
> good) than Python 3!

Who says there's going to be a Python 4? I always assumed 3.9 would be
followed by 3.10.

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#101641

On Thu, 14 Jan 2016 03:25 am, Random832 wrote:

> On Wed, Jan 13, 2016, at 09:21, sjmsoft@gmail.com wrote:
>> This strikes me as very good advice.  Thanks for being so far-sighted.
>> And let's hope that Python 4 has fewer incompatibilities (none would
>> good) than Python 3!
> 
> Who says there's going to be a Python 4? I always assumed 3.9 would be
> followed by 3.10.


Guido has a *very* strong dislike for two digit minor version numbers. It
took a fair amount of arm-twisting to get him to accept two digit micro
version numbers, like 2.7.10. It is doubtful that we'll see 3.10.

But he has definitely ruled that 4.0 (assuming there is one) will not be a
major backwards-incompatible version like 3.0 was.

That's not to say that there won't be any backwards incompatibilities at
all, but they will be relatively minor, like the change from 2.5 to 2.6. (I
bet most people don't even know that 2.6 broke backwards-compatibility.)



-- 
Steven

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#101647

On Wed, Jan 13, 2016 at 10:10 PM, Steven D'Aprano <steve@pearwood.info> wrote:
>  (...) 4.0 (assuming there is one)

Isn't it just a matter of time? Do you think it is even possible not
to have Python 4 eventually?

-- 
Bernardo Sulzbach

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#101654

On Thu, 14 Jan 2016 11:40 am, Bernardo Sulzbach wrote:

> On Wed, Jan 13, 2016 at 10:10 PM, Steven D'Aprano <steve@pearwood.info>
> wrote:
>>  (...) 4.0 (assuming there is one)
> 
> Isn't it just a matter of time? Do you think it is even possible not
> to have Python 4 eventually?

3.9 is probably five or six years away. Perhaps more. A lot can happen in
five years. Just ask Syria.

Maybe Guido will change his mind and we'll have 3.10. 3.11, 3.12, ...

Maybe there will be a sudden and rapid collapse in popularity of Python
between 3.7 and 3.8, and the language is mostly abandoned.

Maybe by the time we approach 3.9, our new xenophobic and fascist overlords
will roll back the internet and ban all that "communist" open source
software, especially those written by foreigners (Dutch or otherwise --
Ruby will be banned too).

Or we're too busy dealing with rising sea levels, crop failures, antibiotic
resistant diseases, chaotic mass migrations, terrorists, wars for control
over resources like water, and the collapse of the corporate state to care
about such little things as upgrades to programming languages.

Or the AI singularity arrives and "human programmer" becomes as obsolete
as "flint knapper".

Or we'll be hit by a big rock from space.

Who knows?




-- 
Steven

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#101656

On 01/13/2016 06:02 PM, Steven D'Aprano wrote:
> Or we're too busy dealing with rising sea levels, crop failures, antibiotic
> resistant diseases, chaotic mass migrations, terrorists, wars for control
> over resources like water, and the collapse of the corporate state to care
> about such little things as upgrades to programming languages.
> 
> Or the AI singularity arrives and "human programmer" becomes as obsolete
> as "flint knapper".

Most likely, given your apocalyptic scenarios, flintknapping will become
an essential skill again!

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#101661

On Thu, 14 Jan 2016 12:02:59 +1100, Steven D'Aprano <steve@pearwood.info>
declaimed the following:

>On Thu, 14 Jan 2016 11:40 am, Bernardo Sulzbach wrote:
>
>> On Wed, Jan 13, 2016 at 10:10 PM, Steven D'Aprano <steve@pearwood.info>
>> wrote:
>>>  (...) 4.0 (assuming there is one)
>> 
>> Isn't it just a matter of time? Do you think it is even possible not
>> to have Python 4 eventually?
>
>3.9 is probably five or six years away. Perhaps more. A lot can happen in
>five years. Just ask Syria.
>
>Maybe Guido will change his mind and we'll have 3.10. 3.11, 3.12, ...
>
	3.14.15926...
-- 
	Wulfraed                 Dennis Lee Bieber         AF6VN
    wlfraed@ix.netcom.com    HTTP://wlfraed.home.netcom.com/

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#101663

On Wednesday 13 January 2016 21:39:12 Dennis Lee Bieber wrote:

> On Thu, 14 Jan 2016 12:02:59 +1100, Steven D'Aprano
> <steve@pearwood.info>
>
> declaimed the following:
> >On Thu, 14 Jan 2016 11:40 am, Bernardo Sulzbach wrote:
> >> On Wed, Jan 13, 2016 at 10:10 PM, Steven D'Aprano
> >> <steve@pearwood.info>
> >>
> >> wrote:
> >>>  (...) 4.0 (assuming there is one)
> >>
> >> Isn't it just a matter of time? Do you think it is even possible
> >> not to have Python 4 eventually?
> >
> >3.9 is probably five or six years away. Perhaps more. A lot can
> > happen in five years. Just ask Syria.
> >
> >Maybe Guido will change his mind and we'll have 3.10. 3.11, 3.12, ...
>
> 	3.14.15926...

Apple, Blueberry or Peach? Preferably ala-mode.

Must....... Learn.......... To........ Resist. I am a DM-II victim. :(
> --
> 	Wulfraed                 Dennis Lee Bieber         AF6VN
>     wlfraed@ix.netcom.com    HTTP://wlfraed.home.netcom.com/


Cheers, Gene Heskett
-- 
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
Genes Web page <http://geneslinuxbox.net:6309/gene>

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#101686

On Wed, 13 Jan 2016 21:59:25 -0500, Gene Heskett <gheskett@wdtv.com>
declaimed the following:

>On Wednesday 13 January 2016 21:39:12 Dennis Lee Bieber wrote:
>
>> On Thu, 14 Jan 2016 12:02:59 +1100, Steven D'Aprano
>> <steve@pearwood.info>
>>
>> declaimed the following:
	<snip>
>> >
>> >Maybe Guido will change his mind and we'll have 3.10. 3.11, 3.12, ...
>>
>> 	3.14.15926...
>
>Apple, Blueberry or Peach? Preferably ala-mode.
>

	Most likely Apple... unless served out in a Dell
-- 
	Wulfraed                 Dennis Lee Bieber         AF6VN
    wlfraed@ix.netcom.com    HTTP://wlfraed.home.netcom.com/

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#101693

Steven D'Aprano wrote:

> Or we'll be hit by a big rock from space.

Sounds like a plan. 

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#101694

On Thu, 14 Jan 2016 14:43:51 +0100
Peter Otten <__peter__@web.de> wrote:
> > Or we'll be hit by a big rock from space.
> 
> Sounds like a plan. 

Which one?  Number 9?

-- 
D'Arcy J.M. Cain
Vybe Networks Inc.
http://www.VybeNetworks.com/
IM:darcy@Vex.Net VoIP: sip:darcy@VybeNetworks.com

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#101697

D'Arcy J.M. Cain wrote:

> On Thu, 14 Jan 2016 14:43:51 +0100
> Peter Otten <__peter__@web.de> wrote:
>> > Or we'll be hit by a big rock from space.
>> 
>> Sounds like a plan.
> 
> Which one?  Number 9?

Hm, I didn't expect this question...

plans[-1], most certainly.

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#101698

On Thu, 14 Jan 2016 16:32:46 +0100
Peter Otten <__peter__@web.de> wrote:
> >> > Or we'll be hit by a big rock from space.
> >> Sounds like a plan.
> > Which one?  Number 9?
> 
> Hm, I didn't expect this question...
> 
> plans[-1], most certainly.

Hmm.  Am I being too subtle or...?

from OuterSpace import plan
print(plan[9])

If that's still too subtle:
https://en.wikipedia.org/wiki/Plan_9_from_Outer_Space

-- 
D'Arcy J.M. Cain
Vybe Networks Inc.
http://www.VybeNetworks.com/
IM:darcy@Vex.Net VoIP: sip:darcy@VybeNetworks.com

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#101703

D'Arcy J.M. Cain wrote:

> On Thu, 14 Jan 2016 16:32:46 +0100
> Peter Otten <__peter__@web.de> wrote:
>> >> > Or we'll be hit by a big rock from space.
>> >> Sounds like a plan.
>> > Which one?  Number 9?
>> 
>> Hm, I didn't expect this question...
>> 
>> plans[-1], most certainly.
> 
> Hmm.  Am I being too subtle or...?

AOL

> from OuterSpace import plan
> print(plan[9])
> 
> If that's still too subtle:
> https://en.wikipedia.org/wiki/Plan_9_from_Outer_Space

OK -- this joke is no more. It has ceased to be. It's expired and gone to 
meet its maker. This is a late joke. It's a stiff. Bereft of life, it rests 
in peace. If you hadn't nailed it to the perch, it would be pushing up the 
daisies. It's rung down the curtain and joined the choir invisible. This is 
an ex-joke.

;)

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#101727

Steven D'Aprano wrote:

> Maybe Guido will change his mind and we'll have 3.10. 3.11, 3.12, ...

Who says that version numbers have to be base 10? After
3.9 we could have 3.A, 3.B, ... 3.Z, and then we have
a long list of Unicode characters to work through before
we're forced to bump the major number up...

-- 
Greg

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#101729

On Fri, Jan 15, 2016 at 2:08 PM, Gregory Ewing
<greg.ewing@canterbury.ac.nz> wrote:
> Steven D'Aprano wrote:
>
>> Maybe Guido will change his mind and we'll have 3.10. 3.11, 3.12, ...
>
>
> Who says that version numbers have to be base 10? After
> 3.9 we could have 3.A, 3.B, ... 3.Z, and then we have
> a long list of Unicode characters to work through before
> we're forced to bump the major number up...

We would have to skip a few - 3.I and 3.O are too confusing, and 3.X
would wreak havoc with people's heads. But then, so would 3.A...

Let's do this. Wreak the havoc. Unleash the folly. Dispel the sanity!

ChrisA

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#101782

Chris Angelico wrote:
> and 3.X would wreak havoc with people's heads.

The danger there is that 3.X would sound so cool (everything
is cooler with an X in it) that nobody would want to move
past it. So after 3.X we would get 3.X.1, ... and then
3.X.X.1, ...

At some point people would start abbreviating those in terms
of powers of X, so the general format of a version number
would become 3.X**m.n where 0 <= n < X.

-- 
Greg

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#101745

On Fri, Jan 15, 2016 at 2:56 AM, Chris Angelico <rosuav@gmail.com> wrote:
>
> We would have to skip a few - 3.I and 3.O are too confusing, and 3.X
> would wreak havoc with people's heads. But then, so would 3.A...
>
> Let's do this. Wreak the havoc. Unleash the folly. Dispel the sanity!
>

There would also be

3.<
3.>
3.=

Not to mention that if the number increased a lot, we would eventually
hit "other numbers" and get 3.<circled one>, etc.

-- 
Bernardo Sulzbach

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#101772

Am 14.01.2016 um 01:40 schrieb Bernardo Sulzbach:
> On Wed, Jan 13, 2016 at 10:10 PM, Steven D'Aprano <steve@pearwood.info> wrote:
>>   (...) 4.0 (assuming there is one)
>
> Isn't it just a matter of time? Do you think it is even possible not
> to have Python 4 eventually?

Not necessarily.
See TeX. :-)

-- 
Robin Koch

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