On Nov 9, 11:37 am, Steven D'Aprano steve
+comp.lang.pyt...@pearwood.info wrote:
On Fri, 09 Nov 2012 17:07:09 +1100, Chris Angelico wrote:
On Fri, Nov 9, 2012 at 12:39 PM, Mark Lawrence breamore...@yahoo.co.uk
wrote:
On 07/11/2012 01:55, Steven D'Aprano wrote:
Who knows? Who cares?
On Sat, Nov 10, 2012 at 2:05 AM, rusi rustompm...@gmail.com wrote:
In x86 assembler
mov ax, 0
is 4 bytes
Three bytes actually, B8 00 00 if my memory hasn't failed me. BA for
DX, B9 ought to be BX and BB CX, I think. But yes, the xor or sub is
two bytes and one clock.
ChrisA
--
Dennis Lee Bieber wrote:
On Fri, 9 Nov 2012 17:07:09 +1100, Chris Angelico ros...@gmail.com
declaimed the following in gmane.comp.python.general:
On Fri, Nov 9, 2012 at 12:39 PM, Mark Lawrence breamore...@yahoo.co.uk
wrote:
On 07/11/2012 01:55, Steven D'Aprano wrote:
Who
Prasad, Ramit wrote:
Dennis Lee Bieber wrote:
Of course, if one has a language that, for some reason, evaluates
right-to-left (APL, anyone), then
x := x - x - x
becomes
x := x - 0
Is that not the same as x:=-x?
No, its the same as 'x = x'.
~Ethan~
--
On 11/07/2012 11:09 PM, Ian Kelly wrote:
On Wed, Nov 7, 2012 at 8:13 PM, Andrew Robinson
andr...@r3dsolutions.com wrote:
OK, and is this a main use case? (I'm not saying it isn't I'm asking.)
I have no idea what is a main use case.
Well, then we can't evaluate if it's worth keeping a list
On Nov 7, 2012, at 11:51 PM, Andrew Robinson andr...@r3dsolutions.com wrote:
On 11/07/2012 04:00 PM, Steven D'Aprano wrote:
Andrew, it appears that your posts are being eaten or rejected by my
ISP's news server, because they aren't showing up for me. Possibly a side-
effect of your dates
On Thu, Nov 8, 2012 at 1:26 AM, Andrew Robinson
andr...@r3dsolutions.com wrote:
OK: Then copy by reference using map:
values = zip( map( lambda:times, xrange(num_groups) ) )
if len(values) len(times) * num_groups ...
Done. It's clearer than a list comprehension and you still really
On Monday, November 5, 2012 3:07:12 PM UTC+8, Chris Rebert wrote:
On Sun, Nov 4, 2012 at 10:27 PM, Demian Brecht demianbre...@gmail.com wrote:
So, here I was thinking oh, this is a nice, easy way to initialize a 4D
matrix (running 2.7.3, non-core libs not allowed):
m = [[None] * 4]
On 07/11/2012 01:55, Steven D'Aprano wrote:
Who knows? Who cares? Nobody does:
n -= n
But I've seen this scattered through code:
x := x - x - x
--
Cheers.
Mark Lawrence.
--
http://mail.python.org/mailman/listinfo/python-list
On Fri, Nov 9, 2012 at 12:39 PM, Mark Lawrence breamore...@yahoo.co.uk wrote:
On 07/11/2012 01:55, Steven D'Aprano wrote:
Who knows? Who cares? Nobody does:
n -= n
But I've seen this scattered through code:
x := x - x - x
Can you enlighten us as to how this is better than either:
x :=
On Fri, 09 Nov 2012 17:07:09 +1100, Chris Angelico wrote:
On Fri, Nov 9, 2012 at 12:39 PM, Mark Lawrence breamore...@yahoo.co.uk
wrote:
On 07/11/2012 01:55, Steven D'Aprano wrote:
Who knows? Who cares? Nobody does:
n -= n
But I've seen this scattered through code:
x := x - x - x
On Fri, Nov 9, 2012 at 5:37 PM, Steven D'Aprano
steve+comp.lang.pyt...@pearwood.info wrote:
On Fri, 09 Nov 2012 17:07:09 +1100, Chris Angelico wrote:
Can you enlighten us as to how this is better than either:
x := -x
or
x := 0 - x
? I'm not seeing it.
I'm hoping that Mark intended it as
On 09/11/2012 06:37, Steven D'Aprano wrote:
On Fri, 09 Nov 2012 17:07:09 +1100, Chris Angelico wrote:
On Fri, Nov 9, 2012 at 12:39 PM, Mark Lawrence breamore...@yahoo.co.uk
wrote:
On 07/11/2012 01:55, Steven D'Aprano wrote:
Who knows? Who cares? Nobody does:
n -= n
But I've seen this
Steven D'Aprano writes:
On Wed, 07 Nov 2012 00:23:44 +, MRAB wrote:
I prefer the term reference semantics.
Oh good, because what the world needs is yet another name for the
same behaviour.
- call by sharing
- call by object sharing
- call by object reference
- call by object
-
Le mercredi 7 novembre 2012 02:55:10 UTC+1, Steven D'Aprano a écrit :
Two-dimensional arrays in Python using lists are quite rare. Anyone who
is doing serious numeric work where they need 2D arrays is using numpy,
not lists. There are millions of people using Python, so it's
On Nov 7, 2012 5:41 AM, Gregory Ewing greg.ew...@canterbury.ac.nz wrote:
If anything is to be done in this area, it would be better
as an extension of list comprehensions, e.g.
[[None times 5] times 10]
which would be equivalent to
[[None for _i in xrange(5)] for _j in xrange(10)]
I
On 7 November 2012 11:11, Oscar Benjamin oscar.j.benja...@gmail.com wrote:
On Nov 7, 2012 5:41 AM, Gregory Ewing greg.ew...@canterbury.ac.nz
wrote:
If anything is to be done in this area, it would be better
as an extension of list comprehensions, e.g.
[[None times 5] times 10]
On 7 November 2012 13:39, Joshua Landau joshua.landau...@gmail.com wrote:
On 7 November 2012 11:11, Oscar Benjamin oscar.j.benja...@gmail.com wrote:
A more modest addition for the limited case described in this thread could
be to use exponentiation:
[0] ** (2, 3)
[[0, 0, 0], [0, 0, 0]]
After this post the only credibility you have left (with me, anyway) is that you seem to be willing
to learn. So learn the way Python works before you try to reimplement it.
~Ethan~
--
http://mail.python.org/mailman/listinfo/python-list
Oscar Benjamin wrote:
On Nov 7, 2012 5:41 AM, Gregory Ewing greg.ew...@canterbury.ac.nz
mailto:greg.ew...@canterbury.ac.nz wrote:
If anything is to be done in this area, it would be better
as an extension of list comprehensions, e.g.
[[None times 5] times 10]
which would be
Gregory Ewing wrote:
Roy Smith wrote:
Call by social network? The called function likes the object.
Depending on how it feels, it can also comment on some of the object's
attributes.
And then finds that it has inadvertently shared all its
private data with other functions accessing
On Nov 7, 2012 3:55 PM, Ethan Furman et...@stoneleaf.us wrote:
Oscar Benjamin wrote:
A more modest addition for the limited case described in this thread
could be to use exponentiation:
[0] ** (2, 3)
[[0, 0, 0], [0, 0, 0]]
What would happen with
-- [{}] ** (2, 3)
The list being
On 2012-11-07 05:05, Steven D'Aprano wrote:
On Wed, 07 Nov 2012 00:23:44 +, MRAB wrote:
Incorrect. Python uses what is commonly known as call-by-object, not
call-by-value or call-by-reference. Passing the list by value would
imply that the list is copied, and that appends or removes to
Hi IAN!
On 11/06/2012 03:52 PM, Ian Kelly wrote:
On Tue, Nov 6, 2012 at 3:41 PM, Andrew Robinson
The objection is not nonsense; you've merely misconstrued it. If
[[1,2,3]] * 4 is expected to create a mutable matrix of 1s, 2s, and
3s, then one would expect [[{}]] * 4 to create a mutable matrix
On Wed, Nov 7, 2012 at 12:51 PM, Andrew Robinson
andr...@r3dsolutions.com wrote:
Interesting, you avoided the main point lists are copied with list
multiplication.
It seems that each post is longer than the last. If we each responded
to every point made, this thread would fill a book.
Anyway,
On 11/06/2012 05:55 PM, Steven D'Aprano wrote:
On Tue, 06 Nov 2012 14:41:24 -0800, Andrew Robinson wrote:
Yes. But this isn't going to cost any more time than figuring out
whether or not the list multiplication is going to cause quirks, itself.
Human psychology *tends* (it's a FAQ!) to
*Spoiler:* You've convinced me.
On 7 November 2012 14:00, Oscar Benjamin oscar.j.benja...@gmail.com wrote:
On 7 November 2012 13:39, Joshua Landau joshua.landau...@gmail.com
wrote:
On 7 November 2012 11:11, Oscar Benjamin oscar.j.benja...@gmail.com
wrote:
A more modest addition for the
On 11/06/2012 10:56 PM, Demian Brecht wrote:
My question was *not* based on what I perceive to be intuitive
(although most of this thread has now seemed to devolve into that and
become more of a philosophical debate), but was based on what I
thought may have been inconsistent behaviour (which
On 07/11/2012 22:02, Andrew Robinson wrote:
You're doing extremely well, you've overtaken Xah Lee as the biggest
waste of space on this list.
--
Cheers.
Mark Lawrence.
--
http://mail.python.org/mailman/listinfo/python-list
On Wed, 07 Nov 2012 17:17:02 +, MRAB wrote:
The disadvantage of calling it call by ... is that it suggests that
you're just talking about calling functions.
*shrug*
There are already two synonyms for this, call by ... and pass by
They are old, venerable terms dating back to Algol
On 7 November 2012 22:16, Joshua Landau joshua.landau...@gmail.com wrote:
On 7 November 2012 14:00, Oscar Benjamin oscar.j.benja...@gmail.com wrote:
On 7 November 2012 13:39, Joshua Landau joshua.landau...@gmail.com
wrote:
On 7 November 2012 11:11, Oscar Benjamin oscar.j.benja...@gmail.com
On Wed, Nov 7, 2012 at 3:02 PM, Andrew Robinson
andr...@r3dsolutions.com wrote:
Draw up some use cases for the multiplication operator (I'm calling on your
experience, let's not trust mine, right?); What are all the Typical ways
people *Do* to use it now?
If those use cases do not
On 11/07/2012 05:39 AM, Joshua Landau wrote:
On 7 November 2012 11:11, Oscar Benjamin wrote:
On Nov 7, 2012 5:41 AM, Gregory Ewing wrote:
If anything is to be done in this area, it would be better
as an extension of list comprehensions, e.g.
[[None times 5]
Andrew, it appears that your posts are being eaten or rejected by my
ISP's news server, because they aren't showing up for me. Possibly a side-
effect of your dates being in the distant past? So if you have replied to
any of my posts, I haven't seen them.
In any case, I wanted to ask a
On 11/07/2012 01:01 PM, Ian Kelly wrote:
On Wed, Nov 7, 2012 at 12:51 PM, Andrew Robinson
andr...@r3dsolutions.com wrote:
Interesting, you avoided the main point lists are copied with list
multiplication.
It seems that each post is longer than the last. If we each responded
to every point
On 8 November 2012 00:00, Steven D'Aprano
steve+comp.lang.pyt...@pearwood.info wrote:
Andrew, it appears that your posts are being eaten or rejected by my
ISP's news server, because they aren't showing up for me. Possibly a side-
effect of your dates being in the distant past? So if you have
On 7 November 2012 23:55, Andrew Robinson andr...@r3dsolutions.com wrote:
On 11/07/2012 05:39 AM, Joshua Landau wrote:
A more modest addition for the limited case described in this thread
could be to use exponentiation:
[0] ** (2, 3)
[[0, 0, 0], [0, 0, 0]]
I'm against over using the
On 08/11/12 12:06, Oscar Benjamin wrote:
On 7 November 2012 22:16, Joshua Landaujoshua.landau...@gmail.com wrote:
That said, losing:
[0] * (2, 3) == [0] * [2, 3]
would mean losing duck-typing in general.
There are precedents for this kind of thing; the
string % operator treats tuples
On 11/07/2012 03:39 PM, Ian Kelly wrote:
Why? Just to get rid of an FAQ?
:-)
Here's one of the more interesting uses from my own code:
OK, and is this a main use case? (I'm not saying it isn't I'm asking.)
Replacing the list multiplication in that function with a list
comprehension would
On Thu, 08 Nov 2012 00:30:53 +, Oscar Benjamin wrote:
Every now and again I come across somebody who tries to distinguish
between call by foo and pass by foo, but nobody has been able to
explain the difference (if any) to me. When you CALL a function, you
PASS values to it. Hence the two
On Wed, 07 Nov 2012 16:24:22 -0800, Andrew Robinson wrote:
On 11/07/2012 01:01 PM, Ian Kelly wrote:
[...]
Anyway, your point was to suggest that people would not be confused by
having list multiplication copy lists but not other objects, because
passing lists into functions as parameters
On 11/07/2012 04:00 PM, Steven D'Aprano wrote:
Andrew, it appears that your posts are being eaten or rejected by my
ISP's news server, because they aren't showing up for me. Possibly a side-
effect of your dates being in the distant past?
Date has been corrected since two days ago. It will
On Wed, Nov 7, 2012 at 8:13 PM, Andrew Robinson
andr...@r3dsolutions.com wrote:
OK, and is this a main use case? (I'm not saying it isn't I'm asking.)
I have no idea what is a main use case.
There is a special keyword which signals the new type of comprehension; A
normal comprehension would
On 11/05/2012 10:07 PM, Chris Angelico wrote:
On Tue, Nov 6, 2012 at 4:51 PM, Andrew Robinson
andr...@r3dsolutions.com wrote:
I really don't think doing a shallow copy of lists would break anyone's
program.
Well, it's a change, a semantic change. It's almost certainly going to
break
On Mon, 05 Nov 2012 21:51:24 -0800, Andrew Robinson wrote:
The most compact notation in programming really ought to reflect the
most *commonly* desired operation. Otherwise, we're really just making
people do extra typing for no reason.
There are many reasons not to put minimizing of typing
On Tue, Nov 6, 2012 at 1:21 AM, Andrew Robinson
andr...@r3dsolutions.com wrote:
If you nest it another time;
[[[None]]]*4, the same would happen; all lists would be independent -- but
the objects which aren't lists would be refrenced-- not copied.
a=[[[alpha,beta]]]*4 would yield:
Well said Steve, I agree with you...
-Shambhu
-Original Message-
From: Steven D'Aprano [mailto:steve+comp.lang.pyt...@pearwood.info]
Sent: Tuesday, November 06, 2012 2:35 PM
To: python-list@python.org
Subject: Re: Multi-dimensional list initialization
On Mon, 05 Nov 2012 21:51:24 -0800
On Nov 6, 2012 6:00 AM, Andrew Robinson andr...@r3dsolutions.com wrote:
On 11/05/2012 06:30 PM, Oscar Benjamin wrote:
stuff = [[obj] * n] * m
I thought that the multiplication of the inner list ([obj] * n) by m
could create a new list of lists using copies. On closer inspection I
see
Ian Kelly wrote:
On Tue, Nov 6, 2012 at 1:21 AM, Andrew Robinson
[snip]
See if you can find *any* python program where people desired the
multiplication to have the die effect that changing an object in one of the
sub lists -- changes all the objects in the other sub lists.
I'm sure
On 11/06/2012 06:35 AM, Oscar Benjamin wrote:
In general, people don't use element multiplication (that I have
*ever* seen) to make lists where all elements of the outer most list
point to the same sub-*list* by reference. The most common use of the
multiplication is to fill an array with
On 11/06/2012 09:32 AM, Prasad, Ramit wrote:
Ian Kelly wrote:
On Tue, Nov 6, 2012 at 1:21 AM, Andrew Robinson
[snip]
See if you can find *any* python program where people desired the
multiplication to have the die effect that changing an object in one of the
sub lists -- changes all the
On 11/06/2012 01:19 AM, Ian Kelly wrote:
On Tue, Nov 6, 2012 at 1:21 AM, Andrew Robinson
If you nest it another time;
[[[None]]]*4, the same would happen; all lists would be independent -- but
the objects which aren't lists would be refrenced-- not copied.
a=[[[alpha,beta]]]*4 would yield:
On Tue, Nov 6, 2012 at 2:36 PM, Andrew Robinson
andr...@r3dsolutions.com wrote:
I meant all lists are shallow copied from the innermost level out.
Equivalently, it's a deep copy of list objects -- but a shallow copy of any
list contents except other lists.
Why only list objects, though? When
On 11/06/2012 01:04 AM, Steven D'Aprano wrote:
On Mon, 05 Nov 2012 21:51:24 -0800, Andrew Robinson wrote:
The most compact notation in programming really ought to reflect the
most *commonly* desired operation. Otherwise, we're really just making
people do extra typing for no reason.
There
Andrew Robinson wrote:
On 11/06/2012 01:04 AM, Steven D'Aprano wrote:
On Mon, 05 Nov 2012 21:51:24 -0800, Andrew Robinson wrote:
[snip]
Q: What about other mutable objects like sets or dicts?
A: No, the elements are never copied.
They aren't list multiplication compatible in
On Tue, Nov 6, 2012 at 3:41 PM, Andrew Robinson
andr...@r3dsolutions.com wrote:
Q: What about other mutable objects like sets or dicts?
A: No, the elements are never copied.
They aren't list multiplication compatible in any event! It's a total
nonsense objection.
If these are
On 2012-11-06 23:52, Ian Kelly wrote:
On Tue, Nov 6, 2012 at 3:41 PM, Andrew Robinson
andr...@r3dsolutions.com wrote:
Q: What about other mutable objects like sets or dicts?
A: No, the elements are never copied.
They aren't list multiplication compatible in any event! It's a total
On Tue, 06 Nov 2012 14:41:24 -0800, Andrew Robinson wrote:
Yes. But this isn't going to cost any more time than figuring out
whether or not the list multiplication is going to cause quirks, itself.
Human psychology *tends* (it's a FAQ!) to automatically assume the
purpose of the list
On Nov 7, 5:26 am, MRAB pyt...@mrabarnett.plus.com wrote:
I prefer the term reference semantics.
Ha! That hits the nail on the head.
To go back to the OP:
On Nov 5, 11:28 am, Demian Brecht demianbre...@gmail.com wrote:
So, here I was thinking oh, this is a nice, easy way to initialize a 4D
On Wed, 07 Nov 2012 00:23:44 +, MRAB wrote:
Incorrect. Python uses what is commonly known as call-by-object, not
call-by-value or call-by-reference. Passing the list by value would
imply that the list is copied, and that appends or removes to the list
inside the function would not
In article 5099ec1d$0$21759$c3e8da3$76491...@news.astraweb.com,
Steven D'Aprano steve+comp.lang.pyt...@pearwood.info wrote:
On Wed, 07 Nov 2012 00:23:44 +, MRAB wrote:
Incorrect. Python uses what is commonly known as call-by-object, not
call-by-value or call-by-reference. Passing
Roy Smith wrote:
Call by social network? The called function likes the object.
Depending on how it feels, it can also comment on some of the object's
attributes.
And then finds that it has inadvertently shared all its
private data with other functions accessing the object.
--
Greg
--
If anything is to be done in this area, it would be better
as an extension of list comprehensions, e.g.
[[None times 5] times 10]
which would be equivalent to
[[None for _i in xrange(5)] for _j in xrange(10)]
--
Greg
--
http://mail.python.org/mailman/listinfo/python-list
On 2012-11-06, at 5:55 PM, Steven D'Aprano
steve+comp.lang.pyt...@pearwood.info wrote:
I'm not entirely sure what your point is here. The OP screwed up -- he
didn't generate a 4-dimensional array. He generated a 2-dimensional
array. If his intuition about the number of dimensions is so
On Mon, Nov 5, 2012 at 6:54 PM, Andrew Robinson
andr...@r3dsolutions.com wrote:
On 11/04/2012 11:27 PM, Chris Angelico wrote:
On Mon, Nov 5, 2012 at 6:07 PM, Chris Rebertc...@rebertia.com wrote:
x = None
x.a = 42
Traceback (most recent call last):
File stdin, line 1, inmodule
On 5/11/12 07:27:52, Demian Brecht wrote:
So, here I was thinking oh, this is a nice, easy way to initialize a 4D
matrix
(running 2.7.3, non-core libs not allowed):
m = [[None] * 4] * 4
The way to get what I was after was:
m = [[None] * 4, [None] * 4, [None] * 4, [None * 4]]
Or
Le lundi 5 novembre 2012 07:28:00 UTC+1, Demian Brecht a écrit :
So, here I was thinking oh, this is a nice, easy way to initialize a 4D
matrix (running 2.7.3, non-core libs not allowed):
m = [[None] * 4] * 4
The way to get what I was after was:
m = [[None] * 4, [None] * 4,
On 2012-11-04, at 10:44 PM, Andrew Robinson andr...@r3dsolutions.com wrote:
but I think you meant:
m = [[None] * 4, [None] * 4, [None] * 4, [None] *4 ]
rather than:
m = [[None] * 4, [None] * 4, [None] * 4, [None * 4]]
Yes, I meant the former, thanks for catching the typo.
Demian Brecht
On 2012-11-04, at 11:07 PM, Chris Rebert c...@rebertia.com wrote:
However, unlike a list object (as in your latter example), the object
`None` is completely immutable (and what's more, a singleton value),
so you just-so-happen *not to be able to* run into the same problem of
mutating an
On 5 November 2012 06:27, Demian Brecht demianbre...@gmail.com wrote:
a = [None] * 4
a[0] = 'a'
a
['a', None, None, None]
m = [[None] * 4] * 4
m[0][0] = 'm'
m
[['m', None, None, None], ['m', None, None, None], ['m', None, None,
None], ['m', None, None, None]]
Is this expected
On 5 November 2012 09:13, Hans Mulder han...@xs4all.nl wrote:
On 5/11/12 07:27:52, Demian Brecht wrote:
So, here I was thinking oh, this is a nice, easy way to initialize a 4D
matrix
(running 2.7.3, non-core libs not allowed):
m = [[None] * 4] * 4
The way to get what I was after was:
m
On Tue, Nov 6, 2012 at 12:32 PM, Oscar Benjamin
oscar.j.benja...@gmail.com wrote:
I was just thinking to myself that it would be a hard thing to change
because the list would need to know how to instantiate copies of all
the different types of the elements in the list. Then I realised it
On 6 November 2012 02:01, Chris Angelico ros...@gmail.com wrote:
On Tue, Nov 6, 2012 at 12:32 PM, Oscar Benjamin
oscar.j.benja...@gmail.com wrote:
I was just thinking to myself that it would be a hard thing to change
because the list would need to know how to instantiate copies of all
the
On 11/05/2012 06:30 PM, Oscar Benjamin wrote:
On 6 November 2012 02:01, Chris Angelicoros...@gmail.com wrote:
On Tue, Nov 6, 2012 at 12:32 PM, Oscar Benjamin
oscar.j.benja...@gmail.com wrote:
I was just thinking to myself that it would be a hard thing to change
because the list would need to
On Tue, Nov 6, 2012 at 4:51 PM, Andrew Robinson
andr...@r3dsolutions.com wrote:
I really don't think doing a shallow copy of lists would break anyone's
program.
Well, it's a change, a semantic change. It's almost certainly going to
break _something_. But for the sake of argument, we can suppose
So, here I was thinking oh, this is a nice, easy way to initialize a 4D
matrix (running 2.7.3, non-core libs not allowed):
m = [[None] * 4] * 4
The way to get what I was after was:
m = [[None] * 4, [None] * 4, [None] * 4, [None * 4]]
(Obviously, I could have just hardcoded the
On 11/04/2012 10:27 PM, Demian Brecht wrote:
So, here I was thinking oh, this is a nice, easy way to initialize a 4D
matrix (running 2.7.3, non-core libs not allowed):
m = [[None] * 4] * 4
The way to get what I was after was:
m = [[None] * 4, [None] * 4, [None] * 4, [None * 4]]
FYI: The
On Sun, Nov 4, 2012 at 10:27 PM, Demian Brecht demianbre...@gmail.com wrote:
So, here I was thinking oh, this is a nice, easy way to initialize a 4D
matrix (running 2.7.3, non-core libs not allowed):
m = [[None] * 4] * 4
The way to get what I was after was:
m = [[None] * 4, [None] * 4,
On Mon, Nov 5, 2012 at 6:07 PM, Chris Rebert c...@rebertia.com wrote:
x = None
x.a = 42
Traceback (most recent call last):
File stdin, line 1, in module
AttributeError: 'NoneType' object has no attribute 'a'
Python needs a YouGottaBeKiddingMeError for times when you do
something utterly
On 11/04/2012 11:27 PM, Chris Angelico wrote:
On Mon, Nov 5, 2012 at 6:07 PM, Chris Rebertc...@rebertia.com wrote:
x = None
x.a = 42
Traceback (most recent call last):
File stdin, line 1, inmodule
AttributeError: 'NoneType' object has no attribute 'a'
Python needs a
Hello I found this very strange; is it a bug, is it a feature, am I
being naughty or what?
foo = [[0, 0], [0, 0]]
baz = [ [0]*2 ] * 2
foo
[[0, 0], [0, 0]]
baz
[[0, 0], [0, 0]]
foo[0][0]=1
baz[0][0]=1
foo
[[1, 0], [0, 0]]
baz
[[1, 0], [1, 0]]
Why on earth does foo and baz behave
[EMAIL PROTECTED] wrote:
Hello I found this very strange; is it a bug, is it a feature, am I
being naughty or what?
foo = [[0, 0], [0, 0]]
baz = [ [0]*2 ] * 2
...
Why on earth does foo and baz behave differently??
This is a frequently made mistake.
try also:
bumble = [[0]*2 for 0 in
[EMAIL PROTECTED] wrote:
Hello I found this very strange; is it a bug, is it a feature, am I
being naughty or what?
the repeat operator (*) creates a new list with references to the same
inner objects, so you end up with a list containing multiple references
to the same list. also see:
An expression like this creates a list of integers:
[0] * 2
[0, 0]
But an expression like this creates list of references to the list
named `foo':
foo = [0, 0]
baz = [foo] * 2
[foo, foo]
So, setting baz[0][0] = 1, is really setting foo[0] = 1. There is only
one instance of foo, but you have
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