Lists & "pointers"

[rixil at hotmail.com]

Jan Danielsson wrote:
> Hello all,
>
>    I have written a simple whiteboard application. In my application, I
> want to be able to set draw attributes. This part works. I have a
> dictionary object which contains stuff like:
> self.attr['Pen.Color'] = ...
> self.attr['Pen.Thickness'] = ...
>
>    Now, the problem is that I want to be able to store attributes in a
> list so they'll be easily accessed using the function keys. I.e. I have
> the "current attributes" which I want to be able to store or retrieve
> in/from a list,
>
> The problem is that I have initialized the list like this:
>
> self.drawAttr = { blah, blah, blah.. }
> self.storedAttr = [ ]
> for i in range(0, 10):
>    self.storedAttr.append(self.drawAttr)
>
>    I know what the problem is; they are all referencing the *same*
> dictionary object. So, my question is: How do I initialize a list of
> dictionary objects, where each list entry is its own object (which is a
> copy from the self.drawAttr object).
>
> Also, how do I store/restore entries to the list?
>
>    I have found the "copy" module, and it's copy method. I assume this
> would work:
>
> for i in range(0, 10):
>    self.storedAttr.append(copy.copy(self.drawAttr))
>
>    However, the concept of "deep copy" confuses me. Do I want it, or
> don't I want it? I repeat: the attributes object is a simple dictionary.
>
> Thankful for any advice.

The easiest way to do it would be to create a new dictionary object for
each iteration of your loop.  In this scenario, you would not need to
use the copy module.

In other words:

self.storedAttr = [ ]
for i in range(0, 10):
    self.storedAttr.append({ blah, blah, blah.. })

I hope this helps!

Regards,

Michael Loritsch