🔒 set of frozensets has duplicate

[broken shuttle]

I want to avoid having duplicate triangles in a list, so I'm trying to use a set.
I wonder why the following two frozensets are added to my set in the first place, as the hashes are invariant of the order:

print("set:", {
  frozenset([Triangle(P(0,0), P(0,1), P(0,2)), Triangle(P(0,1), P(0,3), P(0,2))]),
  frozenset([Triangle(P(0,2), P(0,1), P(0,0)), Triangle(P(0,1), P(0,3), P(0,2))])
})

• P's __hash__ function returns hash((self.x, self.y))
• Triangle's returns hash(frozenset([self.a, self.b, self.c])) (as I want it to be invariant to the order of the three points)
  I'd expect there to be just the first element in the resulting set.

[mighty vector]

@broken shuttle

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[burnt hearth]

I think you need to define __eq__ as well as __hash__.

Post your code.

both for P and for Triangle

[neon dock]

(as I want it to be invariant to the order of the three points)
You could also just use a sorted tuple instead

[broken shuttle]

@dataclasses.dataclass
class P:
    x: int
    y: int
    label: str = ""

    def __repr__(self):
        return f"({self.x},{self.y})"

    def __hash__(self):
        return hash((self.x, self.y))


@dataclasses.dataclass
class Triangle:
    a: P
    b: P
    c: P

    def __repr__(self):
        return f"<{self.a},{self.b},{self.c}>"

    def __hash__(self):
        return hash(frozenset([self.a, self.b, self.c]))

[broken shuttle]

Oh yeah that worked, thanks!

[burnt hearth]

💐

[silent salmon]

You probably should use frozen dataclasses, iirc they even define __hash__ for you

having mutable data inside of sets can lead to weird things

!d dataclasses.dataclass

[mighty vector]

dataclasses.dataclass

@dataclasses.dataclass(*, init=True, repr=True, eq=True, order=False, unsafe_hash=False, frozen=False, match_args=True, kw_only=False, slots=False, weakref_slot=False)```
This function is a [decorator](https://docs.python.org/3/glossary.html#term-decorator) that is used to add generated [special method](https://docs.python.org/3/glossary.html#term-special-method)s to classes, as described below.

The [`dataclass()`](https://docs.python.org/3/library/dataclasses.html#dataclasses.dataclass) decorator examines the class to find `field`s. A `field` is defined as a class variable that has a [type annotation](https://docs.python.org/3/glossary.html#term-variable-annotation). With two exceptions described below, nothing in [`dataclass()`](https://docs.python.org/3/library/dataclasses.html#dataclasses.dataclass) examines the type specified in the variable annotation.

The order of the fields in all of the generated methods is the order in which they appear in the class definition.

[silent salmon]

Having a __hash__() implies that instances of the class are immutable

[mighty vector]

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