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Allow reflected fallback for in-place set operators #9182

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Allow reflected fallback for in-place set operators #9182

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16 changes: 12 additions & 4 deletions crates/vm/src/builtins/set.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1151,7 +1151,9 @@ impl AsNumber for PySet {
}
}),
inplace_subtract: Some(|a, b, vm| {
if let Some(a) = a.downcast_ref::<PySet>() {
if let Some(a) = a.downcast_ref::<PySet>()

@youknowone youknowone Oct 18, 2026

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is there any case PySet but not PyAnySet?

@1ndahous3 1ndahous3 Oct 18, 2026

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the left operand needs to remain a PySet because these slots call mutating PySet::__i*__ methods. PyAnySet would also accept frozenset, which cannot be modified in place. Augmented assignment on a frozenset uses the regular binary operation and reassigns the result instead.

the right operand is only read, so accepting PyAnySet there is appropriate.

&& PyRef::<PyAnySet>::check(b, vm)
{
PySet::__isub__(
a.to_owned(),
PyRef::<PyAnySet>::try_from_object(vm, b.to_owned())?,
Expand All @@ -1163,7 +1165,9 @@ impl AsNumber for PySet {
}
}),
inplace_and: Some(|a, b, vm| {
if let Some(a) = a.downcast_ref::<PySet>() {
if let Some(a) = a.downcast_ref::<PySet>()
&& PyRef::<PyAnySet>::check(b, vm)
{
PySet::__iand__(
a.to_owned(),
PyRef::<PyAnySet>::try_from_object(vm, b.to_owned())?,
Expand All @@ -1175,7 +1179,9 @@ impl AsNumber for PySet {
}
}),
inplace_xor: Some(|a, b, vm| {
if let Some(a) = a.downcast_ref::<PySet>() {
if let Some(a) = a.downcast_ref::<PySet>()
&& PyRef::<PyAnySet>::check(b, vm)
{
PySet::__ixor__(
a.to_owned(),
PyRef::<PyAnySet>::try_from_object(vm, b.to_owned())?,
Expand All @@ -1187,7 +1193,9 @@ impl AsNumber for PySet {
}
}),
inplace_or: Some(|a, b, vm| {
if let Some(a) = a.downcast_ref::<PySet>() {
if let Some(a) = a.downcast_ref::<PySet>()
&& PyRef::<PyAnySet>::check(b, vm)
{
PySet::__ior__(
a.to_owned(),
PyRef::<PyAnySet>::try_from_object(vm, b.to_owned())?,
Expand Down
16 changes: 16 additions & 0 deletions extra_tests/snippets/builtin_set.py
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Original file line number Diff line number Diff line change
@@ -1,3 +1,5 @@
import operator

from testutils import assert_raises

assert set([1, 2]) == set([1, 2])
Expand Down Expand Up @@ -706,3 +708,17 @@ def __del__(self):
intersection_target.intersection_update({1})
assert not intersection_target
assert intersection_events == [True, True]


# Unsupported right operands must reach their reflected set operation.
keys = {2: None, 3: None}.keys()
for method, operation, expected in (
(set.__ior__, operator.ior, {1, 2, 3}),
(set.__iand__, operator.iand, {2}),
(set.__isub__, operator.isub, {1}),
(set.__ixor__, operator.ixor, {1, 3}),
):
source = {1, 2}
assert method(source, keys) is NotImplemented
assert operation(source, keys) == expected
assert source == {1, 2}
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