Python 3 __cmp__ semantic change?

[Johannes Bauer]

Hello group,

I'm porting some code of mine to Python 3. One class has the __cmp__
operator overloaded, but comparison doesn't seem to work anymore with that:

Traceback (most recent call last):
File "./parse", line 25, in <module>
print(x < y)
TypeError: unorderable types: IP() < IP()

Was there some kind of semantic change?

Kind regards,
Johannes

--
"Meine Gegenklage gegen dich lautet dann auf bewusste Verlogenheit,
verlästerung von Gott, Bibel und mir und bewusster Blasphemie."
-- Prophet und Visionär Hans Joss aka HJP in de.sci.physik
<48d8bf1d$0$751 0$5402220f@news .sunrise.ch>

[Inyeol.Lee@gmail.com]

Re: Python 3 __cmp__ semantic change?

On Nov 20, 1:18 pm, Johannes Bauer <dfnsonfsdu...@ gmx.dewrote:

Hello group,
>
I'm porting some code of mine to Python 3. One class has the __cmp__
operator overloaded, but comparison doesn't seem to work anymore with that:
>
Traceback (most recent call last):
  File "./parse", line 25, in <module>
    print(x < y)
TypeError: unorderable types: IP() < IP()
>
Was there some kind of semantic change?

Overload __lt__ method.

Inyeol

[Johannes Bauer]

Re: Python 3 __cmp__ semantic change?

Inyeol.Lee@gmai l.com schrieb:

On Nov 20, 1:18 pm, Johannes Bauer <dfnsonfsdu...@ gmx.dewrote:

>Hello group,
>>
>I'm porting some code of mine to Python 3. One class has the __cmp__
>operator overloaded, but comparison doesn't seem to work anymore with that:
>>
>Traceback (most recent call last):
> File "./parse", line 25, in <module>
> print(x < y)
>TypeError: unorderable types: IP() < IP()
>>
>Was there some kind of semantic change?

>
Overload __lt__ method.

Well, of course I could do that, but the python doc says:

"Called by comparison operations if rich comparison (see above) is not
defined."

http://www.python.org/doc/2.5.2/ref/customization.html

And my code works just fine with 2.5 - only on 3.0 it doesn't work
anymore. Why is that?

Regards,
Johannes

--
"Meine Gegenklage gegen dich lautet dann auf bewusste Verlogenheit,
verlästerung von Gott, Bibel und mir und bewusster Blasphemie."
-- Prophet und Visionär Hans Joss aka HJP in de.sci.physik
<48d8bf1d$0$751 0$5402220f@news .sunrise.ch>

[Christian Heimes]

Re: Python 3 __cmp__ semantic change?

Johannes Bauer wrote:

Hello group,
>
I'm porting some code of mine to Python 3. One class has the __cmp__
operator overloaded, but comparison doesn't seem to work anymore with that:

__cmp__ is gone

Christian

[Steve Holden]

Re: Python 3 __cmp__ semantic change?

Johannes Bauer wrote:

Inyeol.Lee@gmai l.com schrieb:

>On Nov 20, 1:18 pm, Johannes Bauer <dfnsonfsdu...@ gmx.dewrote:

>>Hello group,
>>>
>>I'm porting some code of mine to Python 3. One class has the __cmp__
>>operator overloaded, but comparison doesn't seem to work anymore with that:
>>>
>>Traceback (most recent call last):
>> File "./parse", line 25, in <module>
>> print(x < y)
>>TypeError: unorderable types: IP() < IP()
>>>
>>Was there some kind of semantic change?

>Overload __lt__ method.

>
Well, of course I could do that, but the python doc says:
>
"Called by comparison operations if rich comparison (see above) is not
defined."

http://www.python.org/doc/2.5.2/ref/customization.html

>
And my code works just fine with 2.5 - only on 3.0 it doesn't work
anymore. Why is that?

Well the Python 2.5 documentation can't be regarded as a reliable guide
to what to expect in 3.0 ...

You will observe that __cmp__ no longer appears in the index:

http://docs.python.org/dev/3.0/genindex-_.html

regards
Steve
--
Steve Holden +1 571 484 6266 +1 800 494 3119
Holden Web LLC http://www.holdenweb.com/

[Ben Finney]

Re: Python 3 __cmp__ semantic change?

Steve Holden <steve@holdenwe b.comwrites:

You will observe that __cmp__ no longer appears in the index:
>
http://docs.python.org/dev/3.0/genindex-_.html

I searched in vain for an official description of this changed
behaviour. Where can we find an official description of how
comparisons are different in Python 3.0?

--
\ “[Entrenched media corporations will] maintain the status quo, |
`\ or die trying. Either is better than actually WORKING for a |
_o__) living.” —ringsnake.li vejournal.com, 2007-11-12 |
Ben Finney

[Steve Holden]

Re: Python 3 __cmp__ semantic change?

Ben Finney wrote:

Steve Holden <steve@holdenwe b.comwrites:
>

>You will observe that __cmp__ no longer appears in the index:
>>
>http://docs.python.org/dev/3.0/genindex-_.html

>
I searched in vain for an official description of this changed
behaviour. Where can we find an official description of how
comparisons are different in Python 3.0?
>

If it's not present then it would be worth reporting it as a 3.0 bug -
there's still time to get it in, as the release isn't due until early
December.

regards
Steve
--
Steve Holden +1 571 484 6266 +1 800 494 3119
Holden Web LLC http://www.holdenweb.com/

[Terry Reedy]

Re: Python 3 __cmp__ semantic change?

Ben Finney wrote:

Steve Holden <steve@holdenwe b.comwrites:
>

>You will observe that __cmp__ no longer appears in the index:
>>
>http://docs.python.org/dev/3.0/genindex-_.html

>
I searched in vain for an official description of this changed
behaviour. Where can we find an official description of how
comparisons are different in Python 3.0?

I was going to say "look in "What's New", but the __cmp__ removal is
missing. So I filed

http://bugs.python.org/issue4372

[Christian Heimes]

Re: Python 3 __cmp__ semantic change?

Terry Reedy wrote:

I was going to say "look in "What's New", but the __cmp__ removal is
missing. So I filed
http://bugs.python.org/issue4372

The whatsnew section of Python 3.0 is still empty. Guido didn't had time
to write it. http://bugs.python.org/issue2306

[Johannes Bauer]

Re: Python 3 __cmp__ semantic change?

Steve Holden schrieb:

If it's not present then it would be worth reporting it as a 3.0 bug -
there's still time to get it in, as the release isn't due until early
December.

Seems it was removed on purpose - I'm sure there was a good reason for
that, but may I ask why? Instead of the sleek __cmp__ function I had
earlier, I now have code like:


def __lt__(self, other):
return self.__cmp__(ot her) < 0

def __le__(self, other):
return self.__cmp__(ot her) < 0

def __gt__(self, other):
return self.__cmp__(ot her) 0

def __ge__(self, other):
return self.__cmp__(ot her) >= 0

Does anyone know the reason why __cmp__ was discarded?

Kind regards,
Johannes

--
"Meine Gegenklage gegen dich lautet dann auf bewusste Verlogenheit,
verlästerung von Gott, Bibel und mir und bewusster Blasphemie."
-- Prophet und Visionär Hans Joss aka HJP in de.sci.physik
<48d8bf1d$0$751 0$5402220f@news .sunrise.ch>

[Terry Reedy]

Re: Python 3 __cmp__ semantic change?

Christian Heimes wrote:

Terry Reedy wrote:

>I was going to say "look in "What's New", but the __cmp__ removal is
>missing. So I filed
>http://bugs.python.org/issue4372

>
The whatsnew section of Python 3.0 is still empty. Guido didn't had time
to write it. http://bugs.python.org/issue2306

What's New in Python 3.0 is incomplete but definitely not empty, and it
is part of the doc set.

[skip@pobox.com]

Re: Python 3 __cmp__ semantic change?


JohannesSeems it was removed on purpose - I'm sure there was a good
Johannesreason for that, but may I ask why?

Start here:

http://www.mail-archive.com/python-3000@python.org/msg11474.html

Also, a comment to this blog post suggests creating a CmpMixin:

http://oakwinter.com/code/porting-setuptools-to-py3k/

Skip

[Terry Reedy]

Re: Python 3 __cmp__ semantic change?

Johannes Bauer wrote:

Steve Holden schrieb:
>

>If it's not present then it would be worth reporting it as a 3.0 bug -
>there's still time to get it in, as the release isn't due until early
>December.

>
Seems it was removed on purpose - I'm sure there was a good reason for
that, but may I ask why? Instead of the sleek __cmp__ function I had
earlier, I now have code like:
>
>
def __lt__(self, other):
return self.__cmp__(ot her) < 0
>
def __le__(self, other):
return self.__cmp__(ot her) < 0
>
def __gt__(self, other):
return self.__cmp__(ot her) 0
>
def __ge__(self, other):
return self.__cmp__(ot her) >= 0
>
Does anyone know the reason why __cmp__ was discarded?

See previous threads, including recent one about sorting.

[George Sakkis]

Re: Python 3 __cmp__ semantic change?

On Nov 20, 6:58 pm, s...@pobox.com wrote:

    JohannesSeems it was removed on purpose - I'm sure there was a good
    Johannesreason for that, but may I ask why?
>
Start here:
>
    http://www.mail-archive.com/python-3.../msg11474.html
>
Also, a comment to this blog post suggests creating a CmpMixin:
>
   http://oakwinter.com/code/porting-setuptools-to-py3k/
>
Skip

Dropping __cmp__ without providing implicit or at least easy explicit
[1] total ordering is (was?) a mistake; it opens the door to subtle
bugs or redundant boilerplate code.

[1] E.g. http://code.activestate.com/recipes/576529/

[Duncan Booth]

Re: Python 3 __cmp__ semantic change?

Johannes Bauer <dfnsonfsduifb@ gmx.dewrote:

Seems it was removed on purpose - I'm sure there was a good reason for
that, but may I ask why? Instead of the sleek __cmp__ function I had
earlier, I now have code like:
>
>
def __lt__(self, other):
return self.__cmp__(ot her) < 0
>
def __le__(self, other):
return self.__cmp__(ot her) < 0

I hope you actually have <= here.

>
def __gt__(self, other):
return self.__cmp__(ot her) 0
>
def __ge__(self, other):
return self.__cmp__(ot her) >= 0
>
Does anyone know the reason why __cmp__ was discarded?

I think it was because __cmp__ was the backward compatible fallback for
the newer rich comparison methods and Python 3 cleans up a lot of stuff
left in just for backward compatibility. In this case it is a cleanup
too far as in most cases (i.e. those cases where you don't need the full
complexity of the rich comparisons) __cmp__ is a much simpler solution.

See http://mail.python.org/pipermail/pyt...ch/034073.html
for Guido's original thoughts. Also, once upon a time pep-3000 referred
to the removal of __cmp__ but I can't find it in any of the current
peps. See

http://mail.python.org/pipermail/python-checkins/2004-August/042959.html

and

http://mail.python.org/pipermail/python-checkins/2004-August/042972.html

where the reference to removal of __cmp__ became "Comparison s other than
``==`` and ``!=`` between disparate types will raise an exception unless
explicitly supported by the type" and the reference to Guido's email
about removing __cmp__ was also removed.


--
Duncan Booth http://kupuguy.blogspot.com