On 31 Jul 2009, at 20:48 , Emmanuel Surleau wrote:
On Friday 31 July 2009 19:49:04 Raymond Hettinger wrote:
On Jul 20, 9:27 am, Phillip B Oldham <phillip.old...@gmail.com>
wrote:
Specifically the "differences" between lists and tuples have us
confused and have caused many "discussions" in the office. We
understand that lists are mutable and tuples are not, but we're a
little lost as to why the two were kept separate from the start.
They
both perform a very similar job as far as we can tell.
The underlying C code for the two is substantially the same. In
terms
of code, tuples are in effect just immutable lists that have the
added
feature of being hashable (and therefore usable as dictionary keys or
elements of sets).
Beyond the mutable/hashable distinction, there is an important
philosophical distinction articulated by Guido. He deems tuples
to be useful for struct like groupings of non-homogenous fields
and lists to be useful for sequences of homogenous data suitable
for looping.
While nothing in the list/tuple code requires you to make that
distinction,
it is important because that philosophy pervades the language. If
you
follow Guido's direction, you'll find that the various parts of the
language fit together better. Do otherwise and you'll be going
against
the grain.
I might be wrong, but I get the impression that many people don't
indeed "get
it" and use tuples as static arrays and lists when the array needs
to be
dynamically resized. This is certainly how I use them as well.
This would tend to show that Guido's notion here was not particularly
intuitive.
It's intuitive if you come to Python knowing other languages with
tuples (which are mostly functional, and in which tuples are *never*
sequences/iterables). At the end of the day, and if Guido's intention
truly was what Raymond says, implementing tuples as immutable sequence
was a mistake. And the documentation is to blame as well: in it,
tuples are clearly described as a *sequence* type, not a *structure*
type.
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