nested structure with "internal references"

Hendrik van Rooyen hendrik at
Sat Sep 26 09:10:42 CEST 2009

On Friday, 25 September 2009 19:11:06 Torsten Mohr wrote:

> 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, ...

This sounds terribly convoluted.
What are you trying to do?

> But i'd also like to have something like a "reference" to another
> entry.

Everything and its brother in Python is an object, and things like lists and 
dicts reference objects automagically.

> 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.

Depending on how I read this, it is either trivial or impossible:

A name is bound to an object by assignment.
An object can have many names bound to it.
A name can, at different times, refer to different objects.
An object does not know which names are bound to it, or in what sequence it 
was done.

So you can go from name to object, but not the other way around.
You can use the same name in a loop to refer to different objects, and in each 
iteration, use the name to store a reference to the current object in a list 
or dict.

> Is something like this possible in Python?

Not too sure what you are trying to do.

> 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.

You could start off with a list of lists of lists, to any level of nesting 
that you want.   This will give you a structure like a tree with branches and 
twigs and leaves, but I am not sure if this is what you want or need, or if a 
flat structure like third normal form would suffice, or if you need a 
relational database.

- Hendrik

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