8000 Added support for type guards of the form `x[I] is B` and `x[I] is no… · codemuse-app/scip-python@f1db884 · GitHub
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Added support for type guards of the form x[I] is B and x[I] is not B where x is a tuple and B is a boolean literal True or False. This addresses part of microsoft/pyright#4875.
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3 files changed

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‎docs/type-concepts-advanced.md

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@@ -68,6 +68,7 @@ In addition to assignment-based type narrowing, Pyright supports the following t
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* `x.y == L` and `x.y != L` (where L is a literal expression and x is a type that is distinguished by a field or property with a literal type)
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* `x[K] == V`, `x[K] != V`, `x[K] is V`, and `x[K] is not V` (where K and V are literal expressions and x is a type that is distinguished by a TypedDict field with a literal type)
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* `x[I] == V` and `x[I] != V` (where I and V are literal expressions and x is a known-length tuple that is distinguished by the index indicated by I)
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* `x[I] is B` and `x[I] is not B` (where I is a literal expression, B is a `bool` literal, and x is a known-length tuple that is distinguished by the index indicated by I)
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* `x[I] is None` and `x[I] is not None` (where I is a literal expression and x is a known-length tuple that is distinguished by the index indicated by I)
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* `len(x) == L` and `len(x) != L` (where x is tuple and L is a literal integer)
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* `x in y` or `x not in y` (where y is instance of list, set, frozenset, deque, tuple, dict, defaultdict, or OrderedDict)

‎packages/pyright-internal/src/analyzer/typeGuards.ts

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@@ -277,6 +277,28 @@ export function getTypeNarrowingCallback(
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};
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};
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}
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} else if (ClassType.isBuiltIn(indexType, 'int')) {
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const rightTypeResult = evaluator.getTypeOfExpression(testExpression.rightExpression);
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const rightType = rightTypeResult.type;
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if (
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isClassInstance(rightType) &&
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ClassType.isBuiltIn(rightType, 'bool') &&
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rightType.literalValue !== undefined
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) {
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return (type: Type) => {
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return {
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type: narrowTypeForDiscriminatedTupleComparison(
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evaluator,
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type,
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indexType,
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rightType,
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adjIsPositiveTest
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),
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isIncomplete: !!rightTypeResult.isIncomplete,
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};
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};
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}
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}
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}
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}

‎packages/pyright-internal/src/tests/samples/typeNarrowingTuple1.py

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# This sample tests the type narrowing for known-length tuples
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# that have an entry with a declared literal type.
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from typing import Tuple, Union, Literal
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from typing import Literal
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MsgA = Tuple[Literal[1], str]
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MsgB = Tuple[Literal[2], float]
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MsgA = tuple[Literal[1], str]
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MsgB = tuple[Literal[2], float]
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Msg = Union[MsgA, MsgB]
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MsgAOrB = MsgA | MsgB
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def func1(m: Msg):
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def func1(m: MsgAOrB):
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if m[0] == 1:
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reveal_type(m, expected_text="Tuple[Literal[1], str]")
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reveal_type(m, expected_text="tuple[Literal[1], str]")
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else:
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reveal_type(m, expected_text="Tuple[Literal[2], float]")
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reveal_type(m, expected_text="tuple[Literal[2], float]")
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def func2(m: Msg):
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def func2(m: MsgAOrB):
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if m[0] != 1:
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reveal_type(m, expected_text="Tuple[Literal[2], float]")
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reveal_type(m, expected_text="tuple[Literal[2], float]")
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else:
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reveal_type(m, expected_text="Tuple[Literal[1], str]")
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reveal_type(m, expected_text="tuple[Literal[1], str]")
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MsgC = tuple[Literal[True], str]
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MsgD = tuple[Literal[False], float]
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MsgCOrD = MsgC | MsgD
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def func3(m: MsgCOrD):
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if m[0] is True:
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reveal_type(m, expected_text="tuple[Literal[True], str]")
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else:
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reveal_type(m, expected_text="tuple[Literal[False], float]")
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def func4(m: MsgCOrD):
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if m[0] is not True:
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reveal_type(m, expected_text="tuple[Literal[False], float]")
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else:
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reveal_type(m, expected_text="tuple[Literal[True], str]")

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