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bpo-41064: Improve syntax error for invalid usage of '**' in f-strings #25006

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Merged
pablogsal merged 1 commit into from
Mar 24, 2021
Merged

bpo-41064: Improve syntax error for invalid usage of '**' in f-strings #25006

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2 changes: 2 additions & 0 deletions Grammar/python.gram
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Original file line number Diff line number Diff line change
Expand Up @@ -842,6 +842,8 @@ invalid_for_target:
invalid_group:
| '(' a=starred_expression ')' {
RAISE_SYNTAX_ERROR_KNOWN_LOCATION(a, "can't use starred expression here") }
| '(' a='**' expression ')' {
RAISE_SYNTAX_ERROR_KNOWN_LOCATION(a, "can't use double starred expression here") }
invalid_import_from_targets:
| import_from_as_names ',' {
RAISE_SYNTAX_ERROR("trailing comma not allowed without surrounding parentheses") }
Expand Down
9 changes: 9 additions & 0 deletions Lib/test/test_fstring.py
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Expand Up @@ -1275,5 +1275,14 @@ def test_with_an_underscore_and_a_comma_in_format_specifier(self):
with self.assertRaisesRegex(ValueError, error_msg):
f'{1:_,}'

def test_syntax_error_for_starred_expressions(self):
error_msg = re.escape("can't use starred expression here")
with self.assertRaisesRegex(SyntaxError, error_msg):
compile("f'{*a}'", "?", "exec")

error_msg = re.escape("can't use double starred expression here")
with self.assertRaisesRegex(SyntaxError, error_msg):
compile("f'{**a}'", "?", "exec")

if __name__ == '__main__':
unittest.main()
2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Core and Builtins/2021-03-24-00-32-20.bpo-41064._H0K_g.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,2 @@
Improve the syntax error for invalid usage of double starred elements ('**')
in f-strings. Patch by Pablo Galindo.
35 changes: 34 additions & 1 deletion Parser/parser.c
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Original file line number Diff line number Diff line change
Expand Up @@ -18285,7 +18285,7 @@ invalid_for_target_rule(Parser *p)
return _res;
}

// invalid_group: '(' starred_expression ')'
// invalid_group: '(' starred_expression ')' | '(' '**' expression ')'
static void *
invalid_group_rule(Parser *p)
{
Expand Down Expand Up @@ -18326,6 +18326,39 @@ invalid_group_rule(Parser *p)
D(fprintf(stderr, "%*c%s invalid_group[%d-%d]: %s failed!\n", p->level, ' ',
p->error_indicator ? "ERROR!" : "-", _mark, p->mark, "'(' starred_expression ')'"));
}
{ // '(' '**' expression ')'
if (p->error_indicator) {
D(p->level--);
return NULL;
}
D(fprintf(stderr, "%*c> invalid_group[%d-%d]: %s\n", p->level, ' ', _mark, p->mark, "'(' '**' expression ')'"));
Token * _literal;
Token * _literal_1;
Token * a;
expr_ty expression_var;
if (
(_literal = _PyPegen_expect_token(p, 7)) // token='('
&&
(a = _PyPegen_expect_token(p, 35)) // token='**'
&&
(expression_var = expression_rule(p)) // expression
&&
(_literal_1 = _PyPegen_expect_token(p, 8)) // token=')'
)
{
D(fprintf(stderr, "%*c+ invalid_group[%d-%d]: %s succeeded!\n", p->level, ' ', _mark, p->mark, "'(' '**' expression ')'"));
_res = RAISE_SYNTAX_ERROR_KNOWN_LOCATION ( a , "can't use double starred expression here" );
if (_res == NULL && PyErr_Occurred()) {
p->error_indicator = 1;
D(p->level--);
return NULL;
}
goto done;
}
p->mark = _mark;
D(fprintf(stderr, "%*c%s invalid_group[%d-%d]: %s failed!\n", p->level, ' ',
p->error_indicator ? "ERROR!" : "-", _mark, p->mark, "'(' '**' expression ')'"));
}
_res = NULL;
done:
D(p->level--);
Expand Down