Hi Brian, It sounds like a high quality third-party library that has both a multiset implementation and the itertools you needed would fulfill most of your requirements? Code in the standard library isn't magically of higher quality. Compare eg standard library dataclasses with dataclassy. As a matter of practicality, it might be best if you implemented your ideas as a normal library and after its been proven, you can then lobby for its inclusion in the standard library? (I have only just started contributing to Python. So this is just my opinion. Nothing official.) Cheers, Matthias On Fri, 12 Aug 2022, 23:42 Brian Gladman, <riemannic@gmail.com> wrote:

One of the nice features of capabilities provided in the standard library is a set of data types together with a set of algorithms that that work consistently with them.

For example, we have sequence types that can be used with the itertools module where combinations, combinations_with_replacement, permutations and product are all available.

Being a part of the standard library, these facilities are implemented consistently and their widespread use means that we can have great deal of confidence in their efficiency, effectiveness, reliability and correctness. In short, we can trust them.

Maybe I am on my own here but I make a lot of use of multisets and find that this data type is not well catered for in the Python universe.

There is the counter class in the standard library but it is not a full multiset implementation; there is also a full implementation on PyPy but there are no 'itertools equivalent' algorithms that are designed to work with it. As a result, I am often driven to use, for example, itertools set(permutations(multiset, n)) which is typically very inefficient when compared with a properly implemented multiset permutation algorithm.

And, although there are implementations of various multiset 'itertools algorithms' around, these are 'one-off' pieces of code put together by 'people who needed them' and in which there is little if any solid evidence that they do what they claim to do (some I have tried certainly don't!).

So my plea is for a multiset implementation in the Python standard library (combined witn its itertools equivalent combinatorial algorithms). Being a part of the standard library will bring implementation consistency and widespread use over time will bring us reliability, efficiency, effectiveness and trustworthiness.

Brian Gladman _______________________________________________ Python-ideas mailing list -- python-ideas@python.org To unsubscribe send an email to python-ideas-leave@python.org https://mail.python.org/mailman3/lists/python-ideas.python.org/ Message archived at https://mail.python.org/archives/list/python-ideas@python.org/message/N4EQCC... Code of Conduct: http://python.org/psf/codeofconduct/