This is typically called a "bag". Maybe searching for that will help you find a recipe?
On Tue, May 18, 2010 at 3:13 PM, Gustavo Narea <m...@gustavonarea.net> wrote: > Hello, everybody. > > I've been searching for a data structure like a tuple/list *but* unordered -- > like a set, but duplicated elements shouldn't be removed. I have not even > found a recipe, so I'd like to write an implementation and contribute it to > the "collections" module in the standard library. > > This is the situation I have: I have a data structure that represents an > arithmetic/boolean operation. Operations can be commutative, which means that > the order of their operands don't change the result of the operation. This is, > the following operations are equivalent: > operation(a, b, c) == operation(c, b, a) == operation(b, a, c) > operation(a, b, a) == operation(a, a, b) == operation(b, a, a) > operation(a, a) == operation(a, a) > > So, I need a type to store the arguments/operands so that if two of these > collections have the same elements with the same multiplicity, they are > equivalent, regardless of the order. > > A multiset is not exactly what I need: I still need to use the elements in the > order they were given. For example, the logical conjuction (aka "and" > operator) has a left and right operands; I need to evaluate the first/left one > and, if it returned True, then call the second/right one. They must not be > evaluated in a random order. > > To sum up, it would behave like a tuple or a list, except when it's compared > with another object: They would be equivalent if they're both unordered > tuples/lists, and have the same elements. There can be mutable and immutable > editions (UnorderedList and UnorderedTuple, respectively). > > I will write a PEP to elaborate on this if you think it'd be nice to have. Or, > should I have written the PEP first? > > Cheers, > -- > Gustavo Narea <xri://=Gustavo>. > | Tech blog: =Gustavo/(+blog)/tech ~ About me: =Gustavo/about | > _______________________________________________ > Python-Dev mailing list > Python-Dev@python.org > http://mail.python.org/mailman/listinfo/python-dev > Unsubscribe: > http://mail.python.org/mailman/options/python-dev/guido%40python.org > -- --Guido van Rossum (python.org/~guido) _______________________________________________ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
