python bijection

[geremy condra]

On Fri, Dec 4, 2009 at 2:52 PM, geremy condra <debatem1 at gmail.com> wrote:
> On Fri, Dec 4, 2009 at 11:17 AM, MRAB <python at mrabarnett.plus.com> wrote:
>> M.-A. Lemburg wrote:
>>>
>>> geremy condra wrote:
>>>>
>>>> On Thu, Dec 3, 2009 at 12:57 PM, M.-A. Lemburg <mal at egenix.com> wrote:
>>>>>
>>>>> geremy condra wrote:
>>>>>>
>>>>>> On Thu, Dec 3, 2009 at 7:04 AM, M.-A. Lemburg <mal at egenix.com> wrote:
>>>>>>>
>>>>>>> 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.
>>>>>
>>>>> Thanks for the hint :-)
>>>>>
>>>>> The lib looks nice and would probably serve as a good prototype
>>>>> for writing a new built-in type for Python.
>>>>
>>>> I suspect that it would have a better chance at getting into
>>>> collections than becoming a builtin, but who knows. I'd just
>>>> like to have something like it in the standard library.
>>>
>>> Integrating an easy-to-use graph library into the collections
>>> module (and it's C companion) is good idea.
>>>
>>>>> This would have to be written in C, though,
>>>>
>>>> That's currently in the works, along with database backing.
>>>> We'd welcome any help though... hint, hint...
>>>>
>>>>> and come under a Python compatible license.
>>>>
>>>> I'm willing to dual license under the Python license if
>>>> there were a substantial interest in doing so, and I'm
>>>> confident that the other authors and maintainers
>>>> would feel the same way.
>>>
>>> Great !
>>>
>>>> The question in my mind is whether such an interest exists.
>>>
>>> Since Python is being used more and more in CS classes,
>>> such an addition would complete the tool-set and make Python
>>> even more attractive for undergrad CS courses.
>>>
>>> Finding out how much interest exists in advance is always
>>> a bit difficult with new data-structures. People have to
>>> get a feeling of how they can be put to good use first,
>>> so it's a chicken-and-egg problem.
>>>
>>> We've seen the same thing happen with sets. They were first
>>> made available via a separate module and then became built-ins
>>> after people realized how useful they are in practice.
>>>
>> I'd like to add that people (myself included) were already using dicts
>> for sets before the module was written, so there was already a clear
>> demand for them.
>>

To be fair, I don't think you'd have to look very far to find places
where a graph representation is approximated using some
combination of dicts, sets, and lists. ElementTree comes to mind
immediately, and the dict-of-dicts idea for logging recently
discussed on python-dev explicitly states that it uses that
structure to represent object graphs. To me that says that there
is at least some demand.

Geremy Condra