Re: nested structure with "internal references"
- From: Carl Banks <pavlovevidence@xxxxxxxxx>
- Date: Fri, 25 Sep 2009 11:29:54 -0700 (PDT)
On Sep 25, 10:11 am, Torsten Mohr <tm...@xxxxxxxxxx> wrote:
Hi,
sorry for posting in german before, that was a mistake.
I'd like to use a nested structure in memory that consists
of dict()s and list()s, list entries can be dict()s, other list()s,
dict entries can be list()s or other dict()s.
The lists and dicts can also contain int, float, string, ...
But i'd also like to have something like a "reference" to another
entry.
I'd like to refer to another entry and not copy that entry, i need to
know later that this is a reference to another entry, i need to find
also access that entry then.
Is something like this possible in Python?
The references only need to refer to entries in this structure.
The lists may change at runtime (entries removed / added), so
storing the index may not help.
Hmm, I think I understand what you're asking but I don't think there's
an easy way.
Probably the most straightforward way is to use "cells" of some sort
to contain the entries in a list or dict; then take references to the
cells. That way you can change the cell's value while still
maintaining the reference. For instance, suppose you have a list like
this:
lst = [ 1, 2, 3, 4 ]
Convert it to this:
lst = [ [1], [2], [3], [4] ]
where you are using a nested singleton list as the cell type. Then,
you can take a reference like this:
ref = lst[2]
If you insert an item into the list, the reference remains valid:
lst.insert(0,[0])
And, if you change the value of the cell, the reference will see the
updated value.
lst[3][0] = 5
The downside is that you have to add [0] everywhere. The reference's
value is ref[0], not just ref. The third item in the list is lst[2]
[0], not just lst[2]. You could define custom list- and dict-like
classes that automatically do this, mitigating the problem somewhat.
I hope you could understand that suggestion, it's tough to describe.
Other than that, you are stuck with massive use of Observer pattern
(you'd have to create list- and dict-like types that know when
something is referencing them, and that notify the references whenever
they change).
Carl Banks
.
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