[Python-Dev] Unordered tuples/lists (original) (raw)

Gustavo Narea me at gustavonarea.net
Wed May 19 10:56:03 CEST 2010

Hello, Oleg.

class UnorderedList(list): def eq(self, other): if not isinstance(other, UnorderedList): return False return sorted(self) == sorted(other)

def ne(self, other): return not self.eq(other) Do you need more than that? Oleg.

That's what I had in mind.

I think it'd be useful enough to go in the standard library. Now that there's a sample implementation, should I still try to demonstrate why I believe it's worth adding to the stdlib and get support?

Cheers,

On Tue, May 18, 2010 at 11:13 PM, Gustavo Narea <me at 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 | -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://mail.python.org/pipermail/python-dev/attachments/20100519/217907d1/attachment.html>

More information about the Python-Dev mailing list