Why are frozen multisets in python not considering repeated elements?

Question

I am working with expression trees which are equivalent to each other considering commutativity. To bring about this equivalence, I thought I will use frozen multisets for holding the operands as they are hashable (unlike dicts), unordered (unlike tuples), and allow for repeated elements (unlike sets).

But the frozen multisets don't seem to work as I imagined. They are treating repeated elements as a single element.

Am I missing something here? Please help.

Or please suggest alternatives which serve my purpose. Thanks in advance.

@dudulu I tried print(fms({3,4,3,1}) is fms({1,4,3,3})) and it still returned False.

Solved.

I used a tuple to represent the operands instead of a set. It worked.

`{3,3}` is the same as `{3}` because those are **`set`** literals before any multi-set is constructed. — Davis Herring, Aug 28 '22 at 14:31
You can't, so don't *use* a set. Use something else, like a list. — user2357112, Aug 28 '22 at 14:46
@dudulu: Using `is` makes no sense there. `is` is an object identity test, not an equality test. — user2357112, Aug 28 '22 at 14:47

Josh · Answer 1 · 2022-08-28T14:59:48.650

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As @Davis Herring pointed out, {3,3} notation is for set literals. So the ForcedMultiset treats its contents as a set would. Using tuples (3,3) or lists [3,3] instead solves the problem.

print(fms((3,4,3,1)) == fms((1,4,3,3))) returns True.

edited Aug 28 '22 at 14:59

answered Aug 28 '22 at 14:53

Josh

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More precisely, `fms` receives a 1-element set as its argument; it has no idea what *syntax* was used to create that set. – chepner Aug 28 '22 at 15:06

Why are frozen multisets in python not considering repeated elements?

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