f---ing typechecking

[James Stroud]

Paul McGuire wrote:
> Since tuples are immutable, I think of them as fixed data objects with
> some simple sequential structure, as opposed to lists which are much
> more dynamically accessible/updateable data containers.  Back in my
> relational database design days, I sometimes had to create a primary
> key for a table by combining values stored in two or more columns -
> neither column value alone was unique, but the combination of them
> was, and so made a good retrieval index.  In Python, such data pairs
> would be ideally represented with tuples, in support of in-memory data
> cacheing or tree indexing - for a given record, the values don't
> change, so the immutability of their tupleness doesn't get in the way.
> 
> In similar vein, I've used tuples internally in my Python code as
> cache keys for function memoizing.  They are WORM structures - write
> once, read many - built to represent the cache value, but never
> updated.

> With this idea of tuples as a data structure, I could reasonably
> interpret this:
> 
> (1,"abc",3) + [1]
> 
> to result in (1,"abc",3,[1]) just as well as (1,"abc",3,1).  But
> instead of just picking one, Python complains about this, and so
> forces me to explicitly use
> 
> (1,"abc",3) + tuple([1])
> 
> or
> 
> (1,"abc",3) + ([1],)
> 
> I don't think tuples are just an academic curiosity, as your post
> seems to suggest.
> 
> -- Paul

Were lists implemented as efficiently as tuples in terms of memory and 
speed, there would be no difference except the academic one--which is 
perhaps important.

Actually, I must admit that I use them and their implicit meanings all 
the time in my code (as proof, notice in the "any way to create a 
table-like object?" thread how I specify column headers--its for a 
reason I use tuple in the example because the resulting data structures 
will be ordered according to the tuple passed--of course, I refuse to 
enforce this via "ugly and boring" type checking). For the most part, I 
ignore the implementation differences and draw the distinction at their 
semantics.

Also, risking getting a reputation for being overly contentious, I think 
your argument falls apart in the latter half of your post because "+", 
as far as I can tell with python sequences, is used to mean catenate 
exclusively and not append, which is what you suggest as a possibility.

Anyway, D'Arpano made an excellent point with a good mind-reading 
example and so I understand the design decision regarding catenation of 
tuples and lists more clearly now. I'm still not sure I like it, but 
there is no accounting for taste.

James