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gh-104640: Disallow walrus in comprehension within type scopes #104641

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May 19, 2023
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gh-104640: Disallow walrus in comprehension within type scopes #104641

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3 changes: 3 additions & 0 deletions Lib/test/test_type_params.py
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Original file line number Diff line number Diff line change
Expand Up @@ -136,6 +136,9 @@ def test_disallowed_expressions(self):
check_syntax_error(self, "class X[T: (y := 3)]: pass")
check_syntax_error(self, "class X[T](y := Sequence[T]): pass")
check_syntax_error(self, "def f[T](y: (x := Sequence[T])): pass")
check_syntax_error(self, "class X[T]([(x := 3) for _ in range(2)] and B): pass")
check_syntax_error(self, "def f[T: [(x := 3) for _ in range(2)]](): pass")
check_syntax_error(self, "type T = [(x := 3) for _ in range(2)]")


class TypeParamsNonlocalTest(unittest.TestCase):
Expand Down
35 changes: 31 additions & 4 deletions Python/symtable.c
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Original file line number Diff line number Diff line change
Expand Up @@ -35,6 +35,15 @@
#define NAMED_EXPR_COMP_IN_CLASS \
"assignment expression within a comprehension cannot be used in a class body"

#define NAMED_EXPR_COMP_IN_TYPEVAR_BOUND \
"assignment expression within a comprehension cannot be used in a TypeVar bound"

#define NAMED_EXPR_COMP_IN_TYPEALIAS \
"assignment expression within a comprehension cannot be used in a type alias"

#define NAMED_EXPR_COMP_IN_TYPEPARAM \
"assignment expression within a comprehension cannot be used within the definition of a generic"

#define NAMED_EXPR_COMP_CONFLICT \
"assignment expression cannot rebind comprehension iteration variable '%U'"

Expand Down Expand Up @@ -1857,7 +1866,7 @@ symtable_extend_namedexpr_scope(struct symtable *st, expr_ty e)
}

/* If we find a FunctionBlock entry, add as GLOBAL/LOCAL or NONLOCAL/LOCAL */
if (_PyST_IsFunctionLike(ste)) {
if (ste->ste_type == FunctionBlock) {
long target_in_scope = _PyST_GetSymbol(ste, target_name);
if (target_in_scope & DEF_GLOBAL) {
if (!symtable_add_def(st, target_name, DEF_GLOBAL, LOCATION(e)))
Expand All @@ -1880,9 +1889,27 @@ symtable_extend_namedexpr_scope(struct symtable *st, expr_ty e)

return symtable_add_def_helper(st, target_name, DEF_GLOBAL, ste, LOCATION(e));
}
/* Disallow usage in ClassBlock */
if (ste->ste_type == ClassBlock) {
PyErr_Format(PyExc_SyntaxError, NAMED_EXPR_COMP_IN_CLASS);
/* Disallow usage in ClassBlock and type scopes */
if (ste->ste_type == ClassBlock ||
ste->ste_type == TypeParamBlock ||
ste->ste_type == TypeAliasBlock ||
ste->ste_type == TypeVarBoundBlock) {
switch (ste->ste_type) {
case ClassBlock:
PyErr_Format(PyExc_SyntaxError, NAMED_EXPR_COMP_IN_CLASS);
break;
case TypeParamBlock:
PyErr_Format(PyExc_SyntaxError, NAMED_EXPR_COMP_IN_TYPEPARAM);
break;
case TypeAliasBlock:
PyErr_Format(PyExc_SyntaxError, NAMED_EXPR_COMP_IN_TYPEALIAS);
break;
case TypeVarBoundBlock:
PyErr_Format(PyExc_SyntaxError, NAMED_EXPR_COMP_IN_TYPEVAR_BOUND);
break;
default:
Py_UNREACHABLE();
}
PyErr_RangedSyntaxLocationObject(st->st_filename,
e->lineno,
e->col_offset + 1,
Expand Down