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[3.9] bpo-42374: Allow unparenthesized walrus in genexps (GH-23319) by lysnikolaou · Pull Request #23329 · python/cpython · GitHub

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[3.9] bpo-42374: Allow unparenthesized walrus in genexps (GH-23319) #23329

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Merged
lysnikolaou merged 1 commit into from
Nov 16, 2020
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[3.9] bpo-42374: Allow unparenthesized walrus in genexps (GH-23319) #23329

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2 changes: 1 addition & 1 deletion Grammar/python.gram
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Original file line number Diff line number Diff line change
Expand Up @@ -503,7 +503,7 @@ group[expr_ty]:
| '(' a=(yield_expr | named_expression) ')' { a }
| invalid_group
genexp[expr_ty]:
| '(' a=expression ~ b=for_if_clauses ')' { _Py_GeneratorExp(a, b, EXTRA) }
| '(' a=named_expression ~ b=for_if_clauses ')' { _Py_GeneratorExp(a, b, EXTRA) }
| invalid_comprehension
set[expr_ty]: '{' a=expressions_list '}' { _Py_Set(a, EXTRA) }
setcomp[expr_ty]:
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9 changes: 9 additions & 0 deletions Lib/test/test_named_expressions.py
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Original file line number Diff line number Diff line change
Expand Up @@ -513,6 +513,15 @@ def g():
self.assertEqual(nonlocal_var, None)
f()

def test_named_expression_scope_in_genexp(self):
a = 1
b = [1, 2, 3, 4]
genexp = (c := i + a for i in b)

self.assertNotIn("c", locals())
for idx, elem in enumerate(genexp):
self.assertEqual(elem, b[idx] + a)


if __name__ == "__main__":
unittest.main()
2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Core and Builtins/2020-11-16-17-57-09.bpo-42374.t7np1E.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,2 @@
Fix a regression introduced by the new parser, where an unparenthesized walrus operator
was not allowed within generator expressions.
12 changes: 6 additions & 6 deletions Parser/pegen/parse.c
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Expand Up @@ -11381,7 +11381,7 @@ group_rule(Parser *p)
return _res;
}

// genexp: '(' expression ~ for_if_clauses ')' | invalid_comprehension
// genexp: '(' named_expression ~ for_if_clauses ')' | invalid_comprehension
static expr_ty
genexp_rule(Parser *p)
{
Expand All @@ -11401,12 +11401,12 @@ genexp_rule(Parser *p)
UNUSED(_start_lineno); // Only used by EXTRA macro
int _start_col_offset = p->tokens[_mark]->col_offset;
UNUSED(_start_col_offset); // Only used by EXTRA macro
{ // '(' expression ~ for_if_clauses ')'
{ // '(' named_expression ~ for_if_clauses ')'
if (p->error_indicator) {
D(p->level--);
return NULL;
}
D(fprintf(stderr, "%*c> genexp[%d-%d]: %s\n", p->level, ' ', _mark, p->mark, "'(' expression ~ for_if_clauses ')'"));
D(fprintf(stderr, "%*c> genexp[%d-%d]: %s\n", p->level, ' ', _mark, p->mark, "'(' named_expression ~ for_if_clauses ')'"));
int _cut_var = 0;
Token * _literal;
Token * _literal_1;
Expand All @@ -11415,7 +11415,7 @@ genexp_rule(Parser *p)
if (
(_literal = _PyPegen_expect_token(p, 7)) // token='('
&&
(a = expression_rule(p)) // expression
(a = named_expression_rule(p)) // named_expression
&&
(_cut_var = 1)
&&
Expand All @@ -11424,7 +11424,7 @@ genexp_rule(Parser *p)
(_literal_1 = _PyPegen_expect_token(p, 8)) // token=')'
)
{
D(fprintf(stderr, "%*c+ genexp[%d-%d]: %s succeeded!\n", p->level, ' ', _mark, p->mark, "'(' expression ~ for_if_clauses ')'"));
D(fprintf(stderr, "%*c+ genexp[%d-%d]: %s succeeded!\n", p->level, ' ', _mark, p->mark, "'(' named_expression ~ for_if_clauses ')'"));
Token *_token = _PyPegen_get_last_nonnwhitespace_token(p);
if (_token == NULL) {
D(p->level--);
Expand All @@ -11444,7 +11444,7 @@ genexp_rule(Parser *p)
}
p->mark = _mark;
D(fprintf(stderr, "%*c%s genexp[%d-%d]: %s failed!\n", p->level, ' ',
p->error_indicator ? "ERROR!" : "-", _mark, p->mark, "'(' expression ~ for_if_clauses ')'"));
p->error_indicator ? "ERROR!" : "-", _mark, p->mark, "'(' named_expression ~ for_if_clauses ')'"));
if (_cut_var) {
D(p->level--);
return NULL;
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