On Thu, Dec 3, 2009 at 7:04 AM, M.-A. Lemburg <m...@egenix.com> wrote:
> 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).
If you're in the market for a Python graph library, you may want
to check out Graphine- I'm obviously biased (I wrote most of it)
but it has a few more bells and whistles than kjbuckets, and is
pretty darned easy to use. It also supports undirected and
bridge graphs.
Geremy Condra
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