General question about Python design goals

[Chris Mellon]

On 12/1/05, Christoph Zwerschke <cito at online.de> wrote:
> I think this all boils down to the following:
>
> * In their most frequent use case where tuples are used as lightweight
> data structures keeping together heterogenous values (values with
> different types or meanings), index() and count() do not make much sense.
>
> I completely agree that his is the most frequent case. Still there are
> cases where tuples are used to keep homogenous values together (for
> instance, RGB values, points in space, rows of a matrix). In these cases
> it would be principally useful to have index() and count() methods.
>
> But:
>
> * Very frequently you will use only 2- or 3-tuples, where direct queries
> may be faster than item() and count(). (That's probably why Antoon's RGB
> example was rejected as use case though it was principally a good one).
>
> * Very frequently you want to perform operations on these objects and
> change their elements, so you would use lists instead of tuples anyway.
> See my use case where you would determine whether a vector is zero by
> count()ing its zero entries or the rank of a matrix by count()ing zero rows.
>
> * You will use item() and count() in situations where you are dealing
> with a small discrete range of values in your collection. Often you will
> use strings instead of tuples in these cases, if you don't need to sum()
> the items, for instance.
>
> So, indeed, very few use cases will remain if you filter throught the
> above. But this does not mean that they do not exist. And "special cases
> aren't special enough to break the rules." It should be easy to imagine
> use cases now.
>
> Take for example, a chess game. You are storing the pieces in a
> 64-tuple, where every piece has an integer value corresponding to its
> value in the game (white positive, black negative). You can approximate
> the value of a position by building the sum(). You want to use the tuple
> as a key for a dictionary of stored board constellations (e.g. an
> opening dictionary), therefore you don't use a list.
>

This really looks to me like you have your priorities inverted.
Practically everything you want to do with this structure is
list-like, so why not make it a list and convert it to a tuple when
you need to use it as an index? Even better, since you're doing a lot
of list operations, why not make it a list and define unique IDs or
something to use as indices?

A minor change in your design/thinking (not trying to use a tuple as a
frozen list) instead of a change in the language (making tuples more
like frozen lists) seems to be the warranted solution. But maybe thats
just me.


> Now you want to find the field where the king is standing. Very easy
> with the index() method. Or you want to find the number of pawns on the
> board. Here you could use the count() method.
>
> -- Christoph
> --
> http://mail.python.org/mailman/listinfo/python-list
>