Help, multidimensional list

[Crawley]

Im trying to create a list of lists and for some reason its not working:

class Tile:
_next = { 'n':None, 'ne':None, 'e':None, 'se':None, 's':None,
'sw':None, 'w':None, 'nw':None }


def blankGridCanvas ( maxx, maxy ):
grid = []
for y in xrange( 0, maxy ):
yline = []
for x in xrange( 0, maxx ):
t = Tile()
if y != 0:
t._next[ 'n' ] = grid[ y - 1 ][ x ]
t._next[ 'n' ]._next[ 's' ] = t

yline.append( t )
grid.append( yline )

for y in xrange( 0, maxy ):
for x in xrange( 0, maxx ):
print grid[ x ][ y ], grid[ x ][ y ]._next
return grid

now by my reconing this should be a list of lists with each element being
an instance of Tile, and some references being manipulated to point to each
other. But strangly no, its actually a list of lists where each element is
the SAME instance of Tile, so I change one, i change them ALL!

Whats going on and how do I solve it?

Rich

[Christopher Koppler]

Re: Help, multidimensiona l list

On Sun, 28 Dec 2003 14:27:41 +0000, Crawley
<crawley.storm@ IGetTooMuchSpam AsItIs.com> wrote:
[color=blue]
>Im trying to create a list of lists and for some reason its not working:
>
>class Tile:
> _next = { 'n':None, 'ne':None, 'e':None, 'se':None, 's':None,
>'sw':None, 'w':None, 'nw':None }
>
>
>def blankGridCanvas ( maxx, maxy ):
> grid = []
> for y in xrange( 0, maxy ):
> yline = []
> for x in xrange( 0, maxx ):
> t = Tile()
> if y != 0:
> t._next[ 'n' ] = grid[ y - 1 ][ x ]
> t._next[ 'n' ]._next[ 's' ] = t
>
> yline.append( t )
> grid.append( yline )
>
> for y in xrange( 0, maxy ):
> for x in xrange( 0, maxx ):
> print grid[ x ][ y ], grid[ x ][ y ]._next
> return grid
>
>now by my reconing this should be a list of lists with each element being
>an instance of Tile,[/color]

You only create a *class* Tile, and provide no way to create
*instances* of it - so much like with static variables in other
languages, you only have one 'instance' here. To be able to create
separate instances, you need a constructor in your class to
instantiate every instance, like so:

class Tile:
def __init__(self):
self._next = { 'n':None, 'ne':None, 'e':None, 'se':None,
's':None, 'sw':None, 'w':None, 'nw':None }


and some references being manipulated to point to each[color=blue]
>other. But strangly no, its actually a list of lists where each element is
>the SAME instance of Tile, so I change one, i change them ALL!
>
>Whats going on and how do I solve it?[/color]

Any gurus around can certainly much better explain what's going on and
why...

--
Christopher

[Terry Reedy]

Re: Help, multidimensiona l list


"Christophe r Koppler" <klapotec@chell o.at> wrote in message
news:jbrtuvg9fh 5e0hdj0d6vseo72 87r94sa7d@4ax.c om...[color=blue]
> On Sun, 28 Dec 2003 14:27:41 +0000, Crawley
> <crawley.storm@ IGetTooMuchSpam AsItIs.com> wrote:
>[color=green]
> >Im trying to create a list of lists and for some reason its not working:
> >
> >class Tile:
> > _next = { 'n':None, 'ne':None, 'e':None, 'se':None, 's':None,
> >'sw':None, 'w':None, 'nw':None }
> >
> >
> >def blankGridCanvas ( maxx, maxy ):
> > grid = []
> > for y in xrange( 0, maxy ):
> > yline = []
> > for x in xrange( 0, maxx ):
> > t = Tile()
> > if y != 0:
> > t._next[ 'n' ] = grid[ y - 1 ][ x ]
> > t._next[ 'n' ]._next[ 's' ] = t
> >
> > yline.append( t )
> > grid.append( yline )
> >
> > for y in xrange( 0, maxy ):
> > for x in xrange( 0, maxx ):
> > print grid[ x ][ y ], grid[ x ][ y ]._next
> > return grid
> >
> >now by my reconing this should be a list of lists with each element[/color][/color]
being[color=blue][color=green]
> >an instance of Tile,[/color]
>
> You only create a *class* Tile, and provide no way to create
> *instances* of it[/color]

No, the line 't=Tile()' does create a separate Tile for each grid position.
However, there is only one class attribute shared by all instances.
[color=blue]
> - so much like with static variables in other
> languages, you only have one 'instance' here. To be able to create
> separate instances, you need a constructor in your class to
> instantiate every instance, like so:
>
> class Tile:
> def __init__(self):
> self._next = { 'n':None, 'ne':None, 'e':None, 'se':None,
> 's':None, 'sw':None, 'w':None, 'nw':None }[/color]

You do not need __init__ for separate instances, but do need it to give
each instance its own map.
[color=blue]
> and some references being manipulated to point to each[color=green]
> >other. But strangly no, its actually a list of lists where each element[/color][/color]
is[color=blue][color=green]
> >the SAME instance of Tile, so I change one, i change them ALL![/color][/color]

As stated above, you do have separate instances but only one map attached
to the class instead of a separate map for each instance. Koppler's
__init__ will fix this.

Terry J. Reedy

[Christopher Koppler]

Re: Help, multidimensiona l list

On Sun, 28 Dec 2003 17:50:07 -0500, "Terry Reedy" <tjreedy@udel.e du>
wrote:
[color=blue]
>
>"Christophe r Koppler" <klapotec@chell o.at> wrote in message
>news:jbrtuvg9f h5e0hdj0d6vseo7 287r94sa7d@4ax. com...[color=green]
>> On Sun, 28 Dec 2003 14:27:41 +0000, Crawley
>> <crawley.storm@ IGetTooMuchSpam AsItIs.com> wrote:
>>[color=darkred]
>> >Im trying to create a list of lists and for some reason its not working:
>> >
>> >class Tile:
>> > _next = { 'n':None, 'ne':None, 'e':None, 'se':None, 's':None,
>> >'sw':None, 'w':None, 'nw':None }
>> >
>> >[/color][/color][/color]
[snip some code][color=blue][color=green][color=darkred]
>> >
>> >now by my reconing this should be a list of lists with each element[/color][/color]
>being[color=green][color=darkred]
>> >an instance of Tile,[/color]
>>
>> You only create a *class* Tile, and provide no way to create
>> *instances* of it[/color]
>
>No, the line 't=Tile()' does create a separate Tile for each grid position.
>However, there is only one class attribute shared by all instances.[/color]

Yes, thanks for clearing that up. That is what I probably meant and
didn't know how to say. Too merry Xmas this year ;-)
[color=blue]
>[color=green]
>> - so much like with static variables in other
>> languages, you only have one 'instance' here. To be able to create
>> separate instances, you need a constructor in your class to
>> instantiate every instance, like so:
>>
>> class Tile:
>> def __init__(self):
>> self._next = { 'n':None, 'ne':None, 'e':None, 'se':None,
>> 's':None, 'sw':None, 'w':None, 'nw':None }[/color]
>
>You do not need __init__ for separate instances, but do need it to give
>each instance its own map.[/color]

I think that's what I meant with the comparison to static variables,
but should have read static class attributes.
[color=blue]
>[color=green]
>> and some references being manipulated to point to each[color=darkred]
>> >other. But strangly no, its actually a list of lists where each element[/color][/color]
>is[color=green][color=darkred]
>> >the SAME instance of Tile, so I change one, i change them ALL![/color][/color]
>
>As stated above, you do have separate instances but only one map attached
>to the class instead of a separate map for each instance. Koppler's
>__init__ will fix this.
>
>Terry J. Reedy
>[/color]


--
Christopher