tuple.index()

[Simon Brunning]

On 12/15/06, Christoph Zwerschke <cito at online.de> wrote:
> > If you have a tuple containing, say, a 2d coordinate pair,
>  > and remove something from it, it's no longer a coordinate pair.
>
> Now here comes the ambiguity. If you interpret "x" as "coordinate tuple"
> it would be still one (a 1-tuple), but if you interpret "x" as
> "coordinate pair" then it would indeed not be an "x" any more. So that
> definition is not really helpful.

But the new 1-tuple is no longer usable in the same contexts as the
coordinate pair. In the coordinate pair, you can infer the item's
meaning from its position.

> > A typical example of their combined use is a set of
> > rows returned from a database: each row is a tuple
> > of fields, the same as all other such rows, and removing
> > or adding a field would make no sense. However, add
> > a new row to the list and it remains a list of rows.
>
> Sounds plausible. But when I read a row with the name and forename of a
> person, I might want to collapse the name and forename into one element
> before I hand it over to a function that will display it as a table. Or
> I may want to delete certain elements which are not important. In such
> cases, having each row as list may also make sense.

Sure, you can translate the tuple into a different tuple for a
different purpose, but in terms of the database, only the original
tuple (or other with the same structure) is meaningful.

> The statement "if you are looking for index() or count() for your
> tuples, you're using the wrong container type" is too extreme I think. I
> would agree with "it *may indicate* that you should better use lists".

Oh, absolutely, it's not a hard and fast rule. But I find that if I
try to decide whether to use a tuple or a list based on lists for
homogeneous collections and tuples for heterogeneous collections where
position carries semantic meaning, then I end up using the type that
does what I need. Homogeneous collections often need to be sorted or
searched, wheras heterogeneous collections are often used as
dictionary keys.

-- 
Cheers,
Simon B
simon at brunningonline.net