Hi,
>>None <= 0
True
Why?
Is there a logical reason?
Gregor 17  10199 
On Fri, 25 Apr 2008 20:27:15 +0200
Gregor Horvath <gh@gregor-horvath.comwrote:
>>None <= 0
True
Why?
Why not?
Is there a logical reason?
Everything in Python can compare to everything else. It is up to the
programmer to make sure that they are comparing reasonable things.
--
D'Arcy J.M. Cain <da***@druid.net | Democracy is three wolves http://www.druid.net/darcy/ | and a sheep voting on
+1 416 425 1212 (DoD#0082) (eNTP) | what's for dinner.
Gregor Horvath wrote:
>>None <= 0
True
More accurately:
>>None < 0
True
Why?
Is there a logical reason?
None is "less than" everything except for itself:
>>None < 'a'
True
>>None < False
True
>>None == None
True
In my humble opinion, I think that comparisons involving None should
return None, but I trust that the designers came up with this for very
good reasons. As far as I know I've never been bitten by it.
Paul
D'Arcy J.M. Cain schrieb:
On Fri, 25 Apr 2008 20:27:15 +0200
Gregor Horvath <gh@gregor-horvath.comwrote:
> >>None <= 0
True
Why?
Why not?
Because, from http://www.python.org/dev/peps/pep-0020/ :
Errors should never pass silently.
In the face of ambiguity, refuse the temptation to guess.
Greg
On 2008-04-25, Gregor Horvath <gh@gregor-horvath.comwrote:
Hi,
>None <= 0
True
Why?
Comparing objects of differing types produces an undefined
result. Next time you do it, it might return False. (Well,
it's not really going to, but it's allowed to.)
Is there a logical reason?
For what? There's no reason it returns true rather than false.
The more interesting question is why doesn't it raise an
exception. <ducks>
--
Grant Edwards grante Yow! These PRESERVES should
at be FORCE-FED to PENTAGON
visi.com OFFICIALS!!
On Fri, 25 Apr 2008 11:54:23 -0700
Paul McNett <p@ulmcnett.comwrote:
In my humble opinion, I think that comparisons involving None should
return None...
Like relational databases.
--
D'Arcy J.M. Cain <da***@druid.net | Democracy is three wolves http://www.druid.net/darcy/ | and a sheep voting on
+1 416 425 1212 (DoD#0082) (eNTP) | what's for dinner.
Gregor Horvath wrote:
Hi,
>None <= 0
True
Why?
Is there a logical reason?
Gregor
--
http://mail.python.org/mailman/listinfo/python-list
In early Python, the decision was made that the comparison of *any* two
objects was legal and would return a consistent result. So objects of
different types will compare according to an ordering on their types (an
implementation dependent, unspecified, but consistent ordering), and
objects of the same type will be compared according to rules that make
sense for that type.
Other implementations have the right to compare an integer and None
differently, but on a specific implementation, the result will not change.
Python 3 will raise an exception on such comparisons.
Gary Herron
In my humble opinion, I think that comparisons involving None should
return None, but I trust that the designers came up with this for very
good reasons. As far as I know I've never been bitten by it.
It's fixed in Python 3.x. Python 3.x refuses to compare objects unless
one of both objects has explicit support for both types:
>>1 < None
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: unorderable types: int() < NoneType()
In my humble opinion, I think that comparisons involving None should
return None, but I trust that the designers came up with this for very
good reasons. As far as I know I've never been bitten by it.
It's fixed in Python 3.x. Python 3.x refuses to compare objects unless
one of both objects has explicit support for both types:
>>1 < None
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: unorderable types: int() < NoneType()
On 2008-04-25, D'Arcy J.M. Cain <da***@druid.netwrote:
On Fri, 25 Apr 2008 20:27:15 +0200
Gregor Horvath <gh@gregor-horvath.comwrote:
> >>None <= 0
True
Why?
Why not?
>Is there a logical reason?
Everything in Python can compare to everything else.
Not true.
Python 2.4.4 (#1, Mar 20 2008, 09:20:52) [GCC 3.4.6 (Gentoo 3.4.6-r2, ssp-3.4.6-1.0, pie-8.7.10)] on linux2
>>3j < 7
Traceback (most recent call last):
File "<stdin>", line 1, in ?
TypeError: no ordering relation is defined for complex numbers
It is up to the programmer to make sure that they are
comparing reasonable things.
True.
--
Grant Edwards grante Yow! BEEP-BEEP!! I'm a
at '49 STUDEBAKER!!
visi.com
Grant Edwards <gr****@visi.comwrites:
On 2008-04-25, D'Arcy J.M. Cain <da***@druid.netwrote:
On Fri, 25 Apr 2008 20:27:15 +0200
Gregor Horvath <gh@gregor-horvath.comwrote:
>>None <= 0
True
Everything in Python can compare to everything else.
Not true.
Even more untrue in Python 3.0:
Comparisons other than == and != between disparate types will
raise an exception unless explicitly supported by the type
<URL:http://www.python.org/dev/peps/pep-3100/#core-language>
<URL:http://mail.python.org/pipermail/python-dev/2004-June/045111.html>
--
\ "We demand rigidly defined areas of doubt and uncertainty!" -- |
`\ Vroomfondel, _The Hitch-Hiker's Guide To The Galaxy_, Douglas |
_o__) Adams |
Ben Finney
Gregor Horvath wrote:
D'Arcy J.M. Cain schrieb:
>On Fri, 25 Apr 2008 20:27:15 +0200
Gregor Horvath <gh@gregor-horvath.comwrote:
>> >>None <= 0
True
Why?
Why not?
Because, from http://www.python.org/dev/peps/pep-0020/ :
Errors should never pass silently.
In the face of ambiguity, refuse the temptation to guess.
Greg
Good point.
The problem is the typical one; Python did not originally
have a Boolean type, and the retrofit resulted in weird semantics.
C has the same issue.
John Nagle
=?ISO-8859-15?Q?=22Martin_v=2E_L=F6wis=22?= <ma****@v.loewis.dewrote:
(FWIW, in 2.x, x>=4?, it's None < numbers < anything else;
numbers are ordered by value, everything else is ordered
by type name, then by address, unless comparison functions
are implemented).
Quite apart from Jon pointing out that this isn't true for all cases when
copmparing against None, the other half also isn't true:
>>class C: pass
>>C() < 5
True
That happens at least in Python 2.5.2 on win32. Yet another reason to avoid
old-style classes.
On Apr 29, 5:32 am, Duncan Booth <duncan.bo...@invalid.invalidwrote:
=?ISO-8859-15?Q?=22Martin_v=2E_L=F6wis=22?= <mar...@v.loewis.dewrote:
(FWIW, in 2.x, x>=4?, it's None < numbers < anything else;
numbers are ordered by value, everything else is ordered
by type name, then by address, unless comparison functions
are implemented).
Quite apart from Jon pointing out that this isn't true for all cases when
copmparing against None, the other half also isn't true:
>class C: pass
C() < 5
True
That happens at least in Python 2.5.2 on win32. Yet another reason to avoid
old-style classes.
Sorry - but what are new style classes?
blaine <fr*****@gmail.comwrote:
On Apr 29, 5:32 am, Duncan Booth <duncan.bo...@invalid.invalidwrote:
>=?ISO-8859-15?Q?=22Martin_v=2E_L=F6wis=22?= <mar...@v.loewis.de>
wrote:
(FWIW, in 2.x, x>=4?, it's None < numbers < anything else;
numbers are ordered by value, everything else is ordered
by type name, then by address, unless comparison functions
are implemented).
Quite apart from Jon pointing out that this isn't true for all cases
when copmparing against None, the other half also isn't true:
>>class C: pass
C() < 5
True
That happens at least in Python 2.5.2 on win32. Yet another reason to
avoid old-style classes.
Sorry - but what are new style classes?
New style classes are anything type derived from object. e.g.
class D(object): pass
or (since list is derived from object):
class E(list): pass
Old style classes are those which either have old-style base classes or
no base class at all (and no __metaclass__ either but don't worry about
that for now) e.g. the class C above.
The problem with old style classes is that various things either work
subtly differently or don't work at all, but you don't get much warning.
So basically steer clear of them. An example of something which doesn't
work with old style classes would be the @property decorator: you can
get the property, but setting it simply overwrites the property with the
new value.
See http://www.google.co.uk/search?q=python+%22new+style%22 for more
information.
On Apr 25, 8:17 pm, Jon Ribbens <jon+use...@unequivocal.co.ukwrote:
On 2008-04-25, Martin v. Löwis <mar...@v.loewis.dewrote:
None is smaller than anything.
According to Tim Peters, this is not true.
See http://bugs.python.org/issue1673405
This is unfortunate. I would advocate
something like ordering "incomparable objects"
by the name of their type or something
similar.
When building indexing structures it can be
very nice to be able to construct a list of
heterogeneous tuples and sort them without getting
an exception. Implementing this using L.sort(cmp) where
cmp is implemented in Python can result in
a significant speed penalty.
What's up with Tim Peters anyway? I haven't
seen much from him for a while.
-- Aaron Watters
=== http://www.xfeedme.com/nucular/pydis...ote+tim+peters
"Aaron Watters" <aa***********@gmail.comwrote in message
news:76**********************************@24g2000h sh.googlegroups.com...
|What's up with Tim Peters anyway? I haven't seen much from him for a
while.
I miss him too ;-)
He occasionally responds to tracker or pydev math issues where his unique
knowledge and experience is really needed. (As recently as last Jan).
That is all I know.
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