[Tutor] List index usage: is there a more pythonesque way?

[C M Caine]

Spir sent this solely to me by accident, I think.


---------- Forwarded message ----------
From: spir ☣ <denis.spir at gmail.com>
Date: 2010/4/19
Subject: Re: [Tutor] List index usage: is there a more pythonesque way?
To: cmcaine at googlemail.com


On Mon, 19 Apr 2010 12:59:40 +0100
C M Caine <cmcaine at googlemail.com> wrote:

> That's the first I've read of iterating through dictionaries, I'd
> assumed it was impossible because they're unordered.

Hem, actually "ordered" and "unordered" mean whether the order is
meaningful or not. There are at least 2 implicit orders for each
collection:
* There order in which they where put in.
* The order in which they iterated.
But these can be meaningless, in the sense of arbitrary, like the
alphabetic order. As an example, consider a 'friends' collections:
* If it's just a group of friends, then it's unordered and maps to a
set data structure in python (and computer science, and maths).
* If they are put in the collection eg by favor (best friend first or
last), then it's an ordered *sequence*, and maps to a list data
structure in python (and numerous other languages).
As a consequence, precisely because order is meaningful, another
difference is a sequence can hold several times the same item, while
it makes no sense for a set.

[The choice of the term "list" is imo rather misleading. Eg a shopping
list does not mean one must buy the items in order ;-)]


Denis
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