General question about Python design goals

[Christoph Zwerschke]

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.

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