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gh-152708: Fix AST generation asymmetry for unary positive in match statements #152712

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gh-152708: Fix AST generation asymmetry for unary positive in match statements #152712

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b2f2c25
Fix AST generation asymmetry for unary positive in match statements
Twix1288 Jun 30, 2026
6a7d2f2
Add NEWS entry for gh-152708
Twix1288 Jun 30, 2026
9d7e673
Fix ast.parse validation error for UnaryOp in complex match patterns
Twix1288 Jun 30, 2026
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6 changes: 3 additions & 3 deletions Grammar/python.gram
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Original file line number Diff line number Diff line change
Expand Up @@ -554,20 +554,20 @@ complex_number[expr_ty]:

signed_number[expr_ty]:
| NUMBER
| '+' number=NUMBER { number }
| '+' number=NUMBER { _PyAST_UnaryOp(UAdd, number, EXTRA) }
| '-' number=NUMBER { _PyAST_UnaryOp(USub, number, EXTRA) }

signed_real_number[expr_ty]:
| real_number
| '+' real=real_number { real }
| '+' real=real_number { _PyAST_UnaryOp(UAdd, real, EXTRA) }
| '-' real=real_number { _PyAST_UnaryOp(USub, real, EXTRA) }

real_number[expr_ty]:
| real=NUMBER { _PyPegen_ensure_real(p, real) }

imaginary_number[expr_ty]:
| imag=NUMBER { _PyPegen_ensure_imaginary(p, imag) }
| '+' imag=NUMBER { _PyPegen_ensure_imaginary(p, imag) }
| '+' imag=NUMBER { _PyAST_UnaryOp(UAdd, _PyPegen_ensure_imaginary(p, imag), EXTRA) }

capture_pattern[pattern_ty]:
| target=pattern_capture_target { _PyAST_MatchAs(NULL, target->v.Name.id, EXTRA) }
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1 change: 1 addition & 0 deletions Misc/NEWS.d/next/Core_and_Builtins/2026-06-30-14-50-00.gh-issue-152708.aBcDeF.rst
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@@ -0,0 +1 @@
Fix AST generation asymmetry where unary positive ``+`` was implicitly dropped in pattern match expressions, restoring parsing parity with unary negative ``-``.
42 changes: 39 additions & 3 deletions Parser/parser.c
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17 changes: 11 additions & 6 deletions Python/ast.c
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Original file line number Diff line number Diff line change
Expand Up @@ -426,11 +426,11 @@ ensure_literal_number(expr_ty exp, bool allow_real, bool allow_imaginary)
}

static int
ensure_literal_negative(expr_ty exp, bool allow_real, bool allow_imaginary)
ensure_literal_signed(expr_ty exp, bool allow_real, bool allow_imaginary)
{
assert(exp->kind == UnaryOp_kind);
// Must be negation ...
if (exp->v.UnaryOp.op != USub) {
// Must be negation or positive ...
if (exp->v.UnaryOp.op != USub && exp->v.UnaryOp.op != UAdd) {
return 0;
}
// ... of a constant ...
Expand Down Expand Up @@ -461,7 +461,7 @@ ensure_literal_complex(expr_ty exp)
}
break;
case UnaryOp_kind:
if (!ensure_literal_negative(left, /*real=*/true, /*imaginary=*/false)) {
if (!ensure_literal_signed(left, /*real=*/true, /*imaginary=*/false)) {
return 0;
}
break;
Expand All @@ -476,6 +476,11 @@ ensure_literal_complex(expr_ty exp)
return 0;
}
break;
case UnaryOp_kind:
if (!ensure_literal_signed(right, /*real=*/false, /*imaginary=*/true)) {
return 0;
}
break;
default:
return 0;
}
Expand Down Expand Up @@ -512,9 +517,9 @@ validate_pattern_match_value(expr_ty exp)
// Constants and attribute lookups are always permitted
return 1;
case UnaryOp_kind:
// Negated numbers are permitted (whether real or imaginary)
// Signed numbers are permitted (whether real or imaginary)
// Compiler will complain if AST folding doesn't create a constant
if (ensure_literal_negative(exp, /*real=*/true, /*imaginary=*/true)) {
if (ensure_literal_signed(exp, /*real=*/true, /*imaginary=*/true)) {
return 1;
}
break;
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17 changes: 12 additions & 5 deletions Python/ast_preprocess.c
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Original file line number Diff line number Diff line change
Expand Up @@ -867,26 +867,33 @@ fold_const_match_patterns(expr_ty node, PyArena *ctx_, _PyASTPreprocessState *st
{
case UnaryOp_kind:
{
if (node->v.UnaryOp.op == USub &&
if ((node->v.UnaryOp.op == USub || node->v.UnaryOp.op == UAdd) &&
node->v.UnaryOp.operand->kind == Constant_kind)
{
PyObject *operand = node->v.UnaryOp.operand->v.Constant.value;
PyObject *folded = PyNumber_Negative(operand);
PyObject *folded = node->v.UnaryOp.op == USub ? PyNumber_Negative(operand) : PyNumber_Positive(operand);
if (folded == NULL) {
return 0;
}
return make_const(node, folded, ctx_);
}
break;
}
case BinOp_kind:
{
operator_ty op = node->v.BinOp.op;
if ((op == Add || op == Sub) &&
node->v.BinOp.right->kind == Constant_kind)
if (op == Add || op == Sub)
{
CALL(fold_const_match_patterns, expr_ty, node->v.BinOp.left);
if (node->v.BinOp.left->kind == Constant_kind) {
CALL(fold_const_match_patterns, expr_ty, node->v.BinOp.right);
if (node->v.BinOp.left->kind == Constant_kind &&
node->v.BinOp.right->kind == Constant_kind) {
PyObject *left = node->v.BinOp.left->v.Constant.value;
PyObject *right = node->v.BinOp.right->v.Constant.value;
PyObject *folded = op == Add ? PyNumber_Add(left, right) : PyNumber_Subtract(left, right);
if (folded == NULL) {
return 0;
}
return make_const(node, folded, ctx_);
}
}
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