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?
Gustavo Narea <xri://=Gustavo>.
| Tech blog: =Gustavo/(+blog)/tech ~ About me: =Gustavo/about |