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Groups > comp.lang.python > #6711 > unrolled thread

Something is rotten in Denmark...

Started byharrismh777 <harrismh777@charter.net>
First post2011-05-31 01:48 -0500
Last post2011-06-01 08:40 +1000
Articles 7 on this page of 47 — 13 participants

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  Something is rotten in Denmark... harrismh777 <harrismh777@charter.net> - 2011-05-31 01:48 -0500
    Re: Something is rotten in Denmark... Chris Rebert <clp2@rebertia.com> - 2011-05-31 00:00 -0700
    Re: Something is rotten in Denmark... Ian Kelly <ian.g.kelly@gmail.com> - 2011-05-31 01:35 -0600
    Re: Something is rotten in Denmark... Jussi Piitulainen <jpiitula@ling.helsinki.fi> - 2011-05-31 13:08 +0300
      Re: Something is rotten in Denmark... Thomas Rachel <nutznetz-0c1b6768-bfa9-48d5-a470-7603bd3aa915@spamschutz.glglgl.de> - 2011-05-31 12:48 +0200
        Re: Something is rotten in Denmark... Jussi Piitulainen <jpiitula@ling.helsinki.fi> - 2011-05-31 15:15 +0300
    Re: Something is rotten in Denmark... Terry Reedy <tjreedy@udel.edu> - 2011-05-31 13:11 -0400
      Re: Something is rotten in Denmark... harrismh777 <harrismh777@charter.net> - 2011-05-31 15:18 -0500
        Re: Something is rotten in Denmark... Ian Kelly <ian.g.kelly@gmail.com> - 2011-05-31 16:24 -0600
        Re: Something is rotten in Denmark... Terry Reedy <tjreedy@udel.edu> - 2011-05-31 19:14 -0400
          Re: Something is rotten in Denmark... harrismh777 <harrismh777@charter.net> - 2011-05-31 19:09 -0500
            Re: Something is rotten in Denmark... Terry Reedy <tjreedy@udel.edu> - 2011-06-01 13:11 -0400
              Re: Something is rotten in Denmark... harrismh777 <harrismh777@charter.net> - 2011-06-01 19:40 -0500
                Re: Something is rotten in Denmark... harrismh777 <harrismh777@charter.net> - 2011-06-01 19:50 -0500
                  Re: Something is rotten in Denmark... Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-06-02 04:37 +0000
                Re: Something is rotten in Denmark... Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-06-02 05:14 +0000
                  Re: Something is rotten in Denmark... Chris Angelico <rosuav@gmail.com> - 2011-06-02 18:02 +1000
                  Re: Something is rotten in Denmark... Alain Ketterlin <alain@dpt-info.u-strasbg.fr> - 2011-06-02 13:00 +0200
                    Re: Something is rotten in Denmark... Jussi Piitulainen <jpiitula@ling.helsinki.fi> - 2011-06-02 15:51 +0300
                    Re: Something is rotten in Denmark... Terry Reedy <tjreedy@udel.edu> - 2011-06-02 15:43 -0400
                    Re: Something is rotten in Denmark... Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2011-06-03 11:43 +1200
                      Re: Something is rotten in Denmark... rusi <rustompmody@gmail.com> - 2011-06-02 19:24 -0700
                        Re: Something is rotten in Denmark... Jussi Piitulainen <jpiitula@ling.helsinki.fi> - 2011-06-03 09:17 +0300
                          Re: Something is rotten in Denmark... rusi <rustompmody@gmail.com> - 2011-06-05 03:54 -0700
                            Re: Something is rotten in Denmark... Jussi Piitulainen <jpiitula@ling.helsinki.fi> - 2011-06-05 15:03 +0300
                              Re: Something is rotten in Denmark... rusi <rustompmody@gmail.com> - 2011-06-05 05:26 -0700
                                Re: Something is rotten in Denmark... Jussi Piitulainen <jpiitula@ling.helsinki.fi> - 2011-06-05 16:10 +0300
                      Re: Something is rotten in Denmark... Thomas Rachel <nutznetz-0c1b6768-bfa9-48d5-a470-7603bd3aa915@spamschutz.glglgl.de> - 2011-06-03 10:30 +0200
                        Re: Something is rotten in Denmark... Ian Kelly <ian.g.kelly@gmail.com> - 2011-06-03 11:53 -0600
                      Re: Something is rotten in Denmark... Alain Ketterlin <alain@dpt-info.u-strasbg.fr> - 2011-06-03 12:35 +0200
                        Re: Something is rotten in Denmark... Jussi Piitulainen <jpiitula@ling.helsinki.fi> - 2011-06-03 14:07 +0300
                        Re: Something is rotten in Denmark... harrismh777 <harrismh777@charter.net> - 2011-06-03 15:38 -0500
                        Re: Something is rotten in Denmark... Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2011-06-04 12:40 +1200
                      Re: Something is rotten in Denmark... Nobody <nobody@nowhere.com> - 2011-06-03 14:07 +0100
                  Re: Something is rotten in Denmark... harrismh777 <harrismh777@charter.net> - 2011-06-02 10:44 -0500
                  Re: Something is rotten in Denmark... harrismh777 <harrismh777@charter.net> - 2011-06-02 10:55 -0500
                    Re: Something is rotten in Denmark... Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-06-02 17:22 +0000
                      Re: Something is rotten in Denmark... Ian Kelly <ian.g.kelly@gmail.com> - 2011-06-02 11:43 -0600
                Re: Something is rotten in Denmark... Terry Reedy <tjreedy@udel.edu> - 2011-06-02 02:02 -0400
                  Re: Something is rotten in Denmark... harrismh777 <harrismh777@charter.net> - 2011-06-02 11:02 -0500
    Re: Something is rotten in Denmark... Martin Manns <mmanns@gmx.net> - 2011-05-31 23:14 +0200
      Re: Something is rotten in Denmark... Ian Kelly <ian.g.kelly@gmail.com> - 2011-05-31 15:47 -0600
        Re: Something is rotten in Denmark... Martin Manns <mmanns@gmx.net> - 2011-06-01 02:57 +0200
      Re: Something is rotten in Denmark... harrismh777 <harrismh777@charter.net> - 2011-05-31 16:53 -0500
        Re: Something is rotten in Denmark... harrismh777 <harrismh777@charter.net> - 2011-05-31 17:06 -0500
        Re: Something is rotten in Denmark... Chris Angelico <rosuav@gmail.com> - 2011-06-01 08:39 +1000
        Re: Something is rotten in Denmark... Chris Angelico <rosuav@gmail.com> - 2011-06-01 08:40 +1000

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#6756

FromMartin Manns <mmanns@gmx.net>
Date2011-05-31 23:14 +0200
Message-ID<20110531231456.44d388d7@Fuddel>
In reply to#6711
On Tue, 31 May 2011 01:48:05 -0500
harrismh777 <harrismh777@charter.net> wrote:

> >>> fs=[]
> >>> fs = [(lambda n: i + n) for i in range(10)]
> >>> [fs[i](1) for i in range(10)]
> [10, 10, 10, 10, 10, 10, 10, 10, 10, 10]         <=== not good
> 
>      ( that was a big surprise! . . . )
>      ( let's try it another way . . . )

After being confused I figured out it is a 3.x example:

----

$ python
Python 2.6.6 (r266:84292, Apr 20 2011, 11:58:30) 
[GCC 4.5.2] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> fs=[]
>>> fs = [(lambda n: i + n) for i in range(10)]
>>> [fs[i](1) for i in range(10)]  
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

----

$ python3.1 
Python 3.1.3 (r313:86834, Nov 28 2010, 11:28:10) 
[GCC 4.4.5] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> fs=[]
>>> fs = [(lambda n: i + n) for i in range(10)]
>>> [fs[i](1) for i in range(10)]  
[10, 10, 10, 10, 10, 10, 10, 10, 10, 10]

----

Is this fixed automatically by 2to3?

Martin

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#6757

FromIan Kelly <ian.g.kelly@gmail.com>
Date2011-05-31 15:47 -0600
Message-ID<mailman.2335.1306878486.9059.python-list@python.org>
In reply to#6756
On Tue, May 31, 2011 at 3:14 PM, Martin Manns <mmanns@gmx.net> wrote:
> $ python
> Python 2.6.6 (r266:84292, Apr 20 2011, 11:58:30)
> [GCC 4.5.2] on linux2
> Type "help", "copyright", "credits" or "license" for more information.
>>>> fs=[]
>>>> fs = [(lambda n: i + n) for i in range(10)]
>>>> [fs[i](1) for i in range(10)]
> [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

This works by accident.

>>> [fs[i](1) for i in range(10)]
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
>>> [fs[0](1) for i in range(10)]
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
>>> [f(1) for f in fs]
[10, 10, 10, 10, 10, 10, 10, 10, 10, 10]

The i variable is part of the global scope, and as you iterate over
range(10) again it coincidentally takes on the same values as in the
original list comprehension.  You don't see this in Python 3 because
the scope of i is limited to the list comprehension, not global.

Cheers,
Ian

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#6771

FromMartin Manns <mmanns@gmx.net>
Date2011-06-01 02:57 +0200
Message-ID<mailman.2347.1306889854.9059.python-list@python.org>
In reply to#6757
On Tue, 31 May 2011 15:47:33 -0600
Ian Kelly <ian.g.kelly@gmail.com> wrote:

> The i variable is part of the global scope, and as you iterate over
> range(10) again it coincidentally takes on the same values as in the
> original list comprehension.  You don't see this in Python 3 because
> the scope of i is limited to the list comprehension, not global.

I read about the scope change. 
However, list comprehension scope being global still feels "right" for
me because I am still using Python 2.

I feel that I should start worrying more about future migration issues.

Cheers 

Martin

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#6758

Fromharrismh777 <harrismh777@charter.net>
Date2011-05-31 16:53 -0500
Message-ID<drdFp.23065$iv4.18821@newsfe09.iad>
In reply to#6756
Martin Manns wrote:
> After being confused I figured out it is a 3.x example:

Actually, it is a compatibility example between 2.x and 3.x, compare 
below for different behavior from two seemingly identical compatible 
constructs, one from 3.2, and the other from 2.6.4:


> Python 3.2 (r32:88445, Mar 29 2011, 21:33:57)
> [GCC 4.3.3] on linux2

>>>> fs=[]
>>>> fs = [(lambda n: i + n) for i in range(10)]
>>>> [fs[i](1) for i in range(10)]
> [10, 10, 10, 10, 10, 10, 10, 10, 10, 10]       <=========== compare
>>>>


> Python 2.6.4 (r264:75706, Dec  7 2009, 18:45:15)
> [GCC 4.4.1] on linux2

>>>> fs=[]
>>>> fs = [(lambda n: i + n) for i in range(10)]
>>>> [fs[i](1) for i in range(10)]
> [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]               <=========== compare
>>>>


      Having compared the two, someone please tell me whether the two 
are incompatible, mostly compatible, completely incompatible, or 
different languages...


   ,.,, I realize how 3.2 is working (at the moment) but as compared 
with the books, and the behavior of 2.6, it sure looks 'broke' to me...

... why would we want to defer lookup of the 'i' in range(10) until the 
anonymous function is called, instead of the time that the function 
object is returned... inquiring minds want to know...


PS  Ian calls the second construct "working by mistake..."







kind regards,
m harris

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#6761

Fromharrismh777 <harrismh777@charter.net>
Date2011-05-31 17:06 -0500
Message-ID<RDdFp.20034$4d6.5915@newsfe01.iad>
In reply to#6758
harrismh777 wrote:
> PS  Ian calls the second construct "working by mistake..."

   oops,  actually he called it, "working by accident... "

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#6763

FromChris Angelico <rosuav@gmail.com>
Date2011-06-01 08:39 +1000
Message-ID<mailman.2341.1306881560.9059.python-list@python.org>
In reply to#6758
On Wed, Jun 1, 2011 at 7:53 AM, harrismh777 <harrismh777@charter.net> wrote:
>     Having compared the two, someone please tell me whether the two are
> incompatible, mostly compatible, completely incompatible, or different
> languages...
>

By implication, every version of Python is incompatible with every
other. The 2.7.1 revision notes include:

- Issue #1713: Fix os.path.ismount(), which returned true for symbolic links
  across devices.

Suppose some program were depending on this bug. It works under 2.7.0,
fails under 2.7.1. Does that mean that 2.7.1 is incompatible with
2.7.0?

Chris Angelico

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#6764

FromChris Angelico <rosuav@gmail.com>
Date2011-06-01 08:40 +1000
Message-ID<mailman.2342.1306881605.9059.python-list@python.org>
In reply to#6758
On Wed, Jun 1, 2011 at 8:39 AM, Chris Angelico <rosuav@gmail.com> wrote:
> - Issue #1713: Fix os.path.ismount(), which returned true for symbolic links
>  across devices.

PS. I know nothing about this particular issue, I just skimmed down
the release notes and stopped when something caught my eye. Choose
another example if you know of a better one.

Chris Angelico

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