dictionaries/pointers

[Rob Conner]

I dont know how to do this and can't think of a simple way to.

All I want is a dictionary where two keys point to the same object.
(to steal the ascii art from
http://starship.python.net/crew/mwh/...jectthink.html)
I want sometihng like this:

,------. +-------+
| dict |------>|+-----+| +---+
`------' || "a" |+---->| 1 |
|+-----+| +---+
| | ^
|+-----+| |
|| "b" |+-------'
|+-----+|
+-------+
| |
|+-----+| +---+
|| "c" |+---->| 2 |
|+-----+| +---+
+-------+

Where if I change "a" or "b" to 3 the other one will change?
Is this even possible? How would I do it?

[Erik Max Francis]

Re: dictionaries/pointers

Rob Conner wrote:
[color=blue]
> I dont know how to do this and can't think of a simple way to.
>
> All I want is a dictionary where two keys point to the same object.
> (to steal the ascii art from
> http://starship.python.net/crew/mwh/...jectthink.html)
> I want sometihng like this:
>
> ,------. +-------+
> | dict |------>|+-----+| +---+
> `------' || "a" |+---->| 1 |
> |+-----+| +---+
> | | ^
> |+-----+| |
> || "b" |+-------'
> |+-----+|
> +-------+
> | |
> |+-----+| +---+
> || "c" |+---->| 2 |
> |+-----+| +---+
> +-------+
>
> Where if I change "a" or "b" to 3 the other one will change?
> Is this even possible? How would I do it?[/color]

Objects of type int are immutable in Python, so you'll need a helper
class to do this. Try something like:
[color=blue][color=green][color=darkred]
>>> class Container:[/color][/color][/color]
.... def __init__(self, value=None): self.value = value
.... def get(self): return self.value
.... def set(self, value): self.value = value
....[color=blue][color=green][color=darkred]
>>> one = Container(1)
>>> myDictionary = {}
>>> myDictionary['a'] = one
>>> myDictionary['b'] = one
>>> myDictionary['b'].set(3)
>>> print myDictionary['a'].get()[/color][/color][/color]
3

--
Erik Max Francis && max@alcyone.com && http://www.alcyone.com/max/
San Jose, CA, USA && 37 20 N 121 53 W && AIM erikmaxfrancis
Never make a promise or plan / Take a little love where you can
-- Florence, _Chess_

[Dave Hansen]

Re: dictionaries/pointers

On 7 Oct 2005 14:23:49 -0700, "Rob Conner" <rtconner@gmail .com> wrote:
[color=blue]
>I dont know how to do this and can't think of a simple way to.
>
>All I want is a dictionary where two keys point to the same object.
>(to steal the ascii art from
>http://starship.python.net/crew/mwh/...jectthink.html)
>I want sometihng like this:
>
>,------. +-------+
>| dict |------>|+-----+| +---+
>`------' || "a" |+---->| 1 |
> |+-----+| +---+
> | | ^
> |+-----+| |
> || "b" |+-------'
> |+-----+|
> +-------+
> | |
> |+-----+| +---+
> || "c" |+---->| 2 |
> |+-----+| +---+
> +-------+
>
>Where if I change "a" or "b" to 3 the other one will change?
>Is this even possible? How would I do it?[/color]

A simple, ugly answer: Use a mutable object rather than a plain
integer. Example:
[color=blue][color=green][color=darkred]
>>> elt = [1]
>>> dict = {"a":elt, "b":elt, "c":[2]}
>>> print dict[/color][/color][/color]
{'a': [1], 'c': [2], 'b': [1]}[color=blue][color=green][color=darkred]
>>> dict["a"][0] = 3
>>> print dict[/color][/color][/color]
{'a': [3], 'c': [2], 'b': [3]}[color=blue][color=green][color=darkred]
>>>[/color][/color][/color]

Regards,

-=Dave
--
Change is inevitable, progress is not.