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Fix tuple slice type evaluation for slices with start >= stop #11615

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Fix tuple slice type evaluation for slices with start >= stop #11615

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4 changes: 2 additions & 2 deletions packages/pyright-internal/src/analyzer/tuples.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -550,11 +550,11 @@ export function getSlicedTupleType(
const startValue = getTupleSliceParam(evaluator, sliceNode.d.startValue, 0, tupleTypeArgs);
const endValue = getTupleSliceParam(evaluator, sliceNode.d.endValue, tupleTypeArgs.length, tupleTypeArgs);

if (startValue === undefined || endValue === undefined || endValue < startValue) {
if (startValue === undefined || endValue === undefined) {
return undefined;
}

@rchiodo Rich Chiodo (rchiodo) Aug 13, 2026

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Warning · Non-blocking recommendation

t[True:False] and t[2:1:None] still infer an unbounded tuple instead of tuple[()]. Normalize literal booleans as integer bounds, treat an explicit None step like an omitted step, and add regression assertions for both cases.

[verified]


const slicedTypeArgs = tupleTypeArgs.slice(startValue, endValue);
const slicedTypeArgs = startValue < endValue ? tupleTypeArgs.slice(startValue, endValue) : [];
return ClassType.cloneAsInstance(specializeTupleClass(tupleType, slicedTypeArgs));
}

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15 changes: 15 additions & 0 deletions packages/pyright-internal/src/tests/samples/tuple20.py
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@@ -0,0 +1,15 @@
# Sample test for tuple slicing with start index >= stop index.

t: tuple[int, str, bool] = (1, "a", True)

# Slicing where start >= stop produces an empty tuple (tuple[()])
# in Python runtime.

a = t[2:1]
reveal_type(a, expected_text="tuple[()]")

b = t[-1:-2]
reveal_type(b, expected_text="tuple[()]")

c = t[5:1]
reveal_type(c, expected_text="tuple[()]")

@rchiodo Rich Chiodo (rchiodo) Aug 13, 2026

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Warning · Non-blocking recommendation

tuple13.py already owns tuple slice-expression coverage, including empty and reversed slices. Move these cases there and remove the additional sample registration so the behavior remains specified in one place.

[verified]

6 changes: 6 additions & 0 deletions packages/pyright-internal/src/tests/typeEvaluator8.test.ts
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Expand Up @@ -610,6 +610,12 @@ test('Tuple19', () => {
TestUtils.validateResults(analysisResults, 1);
});

test('Tuple20', () => {
const analysisResults = TestUtils.typeAnalyzeSampleFiles(['tuple20.py']);

TestUtils.validateResults(analysisResults, 0);
});

test('NamedTuple1', () => {
const analysisResults = TestUtils.typeAnalyzeSampleFiles(['namedTuple1.py']);

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