[subotac]

Fixes #16115.

set.__xor__ and frozenset.__xor__ return NotImplemented for arbitrary collections.abc.Set implementations, allowing reflected dispatch to determine the result type. Preserve the concrete return type
for built-in set operands and return AbstractSet for the general case.

The new test covers both built-in left operands with an abstract set right operand.

[OutSquareCapital]

To be 100% correct the input type should be widened to Iterable. The default implementation of AbstractSet handles them

[JelleZijlstra]

This seems incorrect, set.__xor__ doesn't return this. It only accepts set and frozenset. xor with AbstractSets instead works through an __rxor__ method on those other sets.

[subotac]

Updated the builtin signatures to accept only set/frozenset and added AbstractSet.rxor for reflected dispatch; the regression test checks both paths. Could you take another look?

[OutSquareCapital]

My comment was completely ignored, but I'm insisting on the fact that AbstractSet inputs should be widened to Iterable. Most are currently incorrectly constrained to AbstractSet.

the actual code:

    def __and__(self, other):
        if not isinstance(other, Iterable):
            return NotImplemented
        return self._from_iterable(value for value in other if value in self)

    __rand__ = __and__

    def isdisjoint(self, other):
        """Return True if two sets have a null intersection."""
        for value in other:
            if value in self:
                return False
        return True

    def __or__(self, other):
        if not isinstance(other, Iterable):
            return NotImplemented
        chain = (e for s in (self, other) for e in s)
        return self._from_iterable(chain)

    __ror__ = __or__

    def __sub__(self, other):
        if not isinstance(other, Set):
            if not isinstance(other, Iterable):
                return NotImplemented
            other = self._from_iterable(other)
        return self._from_iterable(value for value in self if value not in other)

    def __rsub__(self, other):
        if not isinstance(other, Set):
            if not isinstance(other, Iterable):
                return NotImplemented
            other = self._from_iterable(other)
        return self._from_iterable(value for value in other if value not in self)

    def __xor__(self, other):
        if not isinstance(other, Set):
            if not isinstance(other, Iterable):
                return NotImplemented
            other = self._from_iterable(other)
        return (self - other) | (other - self)

    __rxor__ = __xor__

rxor having a signature different to xor don't make sense here. The rxor simply defer to xor.

[subotac]

The local conflict resolution preserves the newer reflected overloads and restores reflected XOR support for AbstractSet The focused typing checks pass. The update has not been pushed yet

[github-actions]

According to mypy_primer, this change has no effect on the checked open source code. 🤖🎉

[srittau]

Thanks!