Raymond Hettinger wrote:
> [Joshua Bronson]
>> Raymond, do you think there might be any future in including a built-
>> in bidict data structure in Python?
>
> I don't think so. There are several forces working against it:
>
> * the recipe is new, so it hasn't had a chance to mature
> or to gain a fan club.
>
> * there are many approaches to the solving the problem and
> there is no reason to assume this one is the best.
>
> * it extends the language with arcane syntax tricks instead of
> using the language as designed by Guido. That makes it harder
> to learn and remember.
>
> * we've already got one (actually two). The two dictionary approach
> uses plain python, requires no new learning, and is more flexible.
> Also, sqlite3 provides another way to use multiple lookups to a
> single record. The database approach is much more general
> (extending to trijections, allowing multiple sort orders,
> providing persistence, etc).
>
> * the semantics of a bijection aren't obvious:
>
> b['x'] = 'ex' # first record: ('x', 'ex')
> b['y'] = 'why' # second record: ('y', 'why')
> b[:'why'] = 'x' # do two records collapse into one? is there
> an error?
>
> * the proposed syntax doesn't address the issue covered in my previous
> post.
> Since bijections are symmetrical, they do not have an obvious
> direction
> (which is the primary key, the husband or the wife?). The syntax
> needs to
> allow user names to make it clear which is being accessed:
>
> marriages.h2w['john'] = 'amy'
> marriages.w2h['amy'] = 'john'
>
> Contrast this with:
>
> marriages['jordan'] = 'taylor' # are you sure you got the
> order correct?
> marriages[:'taylor'] = 'jordan' # this is easy to get backwards
I think the only major CS data type missing from Python is some
form of (fast) directed graph implementation à la kjGraph:
http://gadfly.sourceforge.net/kjbuckets.html
With these, you can easily build all sorts of relations between
objects and apply fast operations on them. In fact, it should then
be possible to build a complete relational database in Python
(along the lines of Gadfly).
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