Odd list behaviour

[Moritz B]

Hi!
I'm coding a program that's supposed to solve Sudoku, but came accross a really odd behaviour of lists.

comparelist is a 2D list (9 x 9) filled with integers and unsorted (and I want it to stay that way)

>for i in range(9):
>>> bufferlist=comp arelist[i]
>>> bufferlist=sort er.sortiere(buf ferlist,0,len(b ufferlist)-1) # sorts a list
>>> if bufferlist==che cklist:
>>>>> count2=count2+1
>print comparelist

now, the bufferlists are all being sorted properly, but the comparelist is now sorted as well !! Why is that so? I really don't understand that behaviour, since I don't say to put the sorted bufferlist back into the comparelist.

Someone help me please. And thanks in advance :)

~Mo

[kudos]

Hi!
you buffer points to the list inside your 2d list, what you need to do is to make your own version of the list.

Something like this perhaps?
import copy
bufferlist=copy .copy(compareli st[i])

-kudos

Hi!
I'm coding a program that's supposed to solve Sudoku, but came accross a really odd behaviour of lists.

comparelist is a 2D list (9 x 9) filled with integers and unsorted (and I want it to stay that way)

>for i in range(9):
>>> bufferlist=comp arelist[i]
>>> bufferlist=sort er.sortiere(buf ferlist,0,len(b ufferlist)-1) # sorts a list
>>> if bufferlist==che cklist:
>>>>> count2=count2+1
>print comparelist

now, the bufferlists are all being sorted properly, but the comparelist is now sorted as well !! Why is that so? I really don't understand that behaviour, since I don't say to put the sorted bufferlist back into the comparelist.

Someone help me please. And thanks in advance :)

~Mo

[Moritz B]

I'll try that. Thanks alot.

~Mo

[Moritz B]

Ok it's all working now, thanks again. Just need to do sth about my algorithm now... going through 10 ^ 81 possibilities, of which a bazillion are totally irrelevant, by brute force just isn't quite the right thing :P
Anyway it works if u put in like de first 76 numbers... u'd only have to wait about a minute then, till de program pops up with an answer... hehe (^ - ^')

But back to the topic. Wouldn't one expect, just by intuition or whatever, that if u write
>list1=list2
both lists would be totally handled individually afterwards? I don't get why there have to be these 'pointers'. Well, I guess it's probably needed for sum advanced programming or more complex coding. But if anyone could dumb it down and explain to me as to why and for what purpose these links between the lists exist I'd be very grateful.

~Mo

[kudos]

Hi!
the trick to make sudoku solving faster, is to perform some heuristic before you do
the exhaustive search. This page present some 'heuristics' :
http://www.javaonthebr ain.com/java/sudokuspoiler/technical.html in a nice and
graphical way.

I don't really know the 'computer science' reason why the list doesn't get copied
when you do
list2 = list1
but i would guess it might have something to do with saving memory. An example, one of
the cool features with the C programming language is the following;

assume I have the list

unsigned int a[] = {0xff00cc00,0x0 0ffccaa};

Now, lets assume that I want the first byte in the second entry in the array, then
I could add the following line;

unsigned char *b;
b = (unsigned char *)a;
printf("%d\n",b[5]);

Now isn't it a bit irritating, if this automatical should 'steal' 8 bytes of memory, by
allocating space for b?`

Another example is the following, lets assume that you have a list, that you want to
sort:

list = 5,3,2,6,1,4
sort(list)

wouldn't it be kind of irritating, if this command didn't sort 'list', but instead
returned a new list?

A last note, in my last post I mentioned the following;
list = [1,2,3,4,5,6]
if, you could use copy to do the following;
list2 = copy.copy(list)
However, I noticed that you said that you where working with 2d list, maybe
something like this:

list1 = [[1,2],[3,4],[5,6]]

what if we copy this list too?

list2 = copy.copy(list1 )

Now try to change

list2[0][1] = 7

then list2 would be [[1,7],[3,4],[5,6]], but this would also be content of list1!

Ok it's all working now, thanks again. Just need to do sth about my algorithm now... going through 10 ^ 81 possibilities, of which a bazillion are totally irrelevant, by brute force just isn't quite the right thing :P
Anyway it works if u put in like de first 76 numbers... u'd only have to wait about a minute then, till de program pops up with an answer... hehe (^ - ^')

But back to the topic. Wouldn't one expect, just by intuition or whatever, that if u write
>list1=list2
both lists would be totally handled individually afterwards? I don't get why there have to be these 'pointers'. Well, I guess it's probably needed for sum advanced programming or more complex coding. But if anyone could dumb it down and explain to me as to why and for what purpose these links between the lists exist I'd be very grateful.

~Mo