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bpo-44947: Refine the syntax error for trailing commas in import statements #27814

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Merged
merged 1 commit into from
Aug 18, 2021
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bpo-44947: Refine the syntax error for trailing commas in import statements #27814

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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 @@ -1169,7 +1169,7 @@ invalid_group:
| '(' a='**' expression ')' {
RAISE_SYNTAX_ERROR_KNOWN_LOCATION(a, "cannot use double starred expression here") }
invalid_import_from_targets:
| import_from_as_names ',' {
| import_from_as_names ',' NEWLINE {
RAISE_SYNTAX_ERROR("trailing comma not allowed without surrounding parentheses") }

invalid_with_stmt:
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7 changes: 7 additions & 0 deletions Lib/test/test_syntax.py
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Expand Up @@ -1202,6 +1202,13 @@
Traceback (most recent call last):
SyntaxError: trailing comma not allowed without surrounding parentheses

# Check that we dont raise the "trailing comma" error if there is more
# input to the left of the valid part that we parsed.

>>> from t import x,y, and 3
Traceback (most recent call last):
SyntaxError: invalid syntax

>>> (): int
Traceback (most recent call last):
SyntaxError: only single target (not tuple) can be annotated
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2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Core and Builtins/2021-08-18-19-09-28.bpo-44947.mcvGdS.rst
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@@ -0,0 +1,2 @@
Refine the syntax error for trailing commas in import statements. Patch by
Pablo Galindo.
13 changes: 8 additions & 5 deletions Parser/parser.c
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Expand Up @@ -19540,7 +19540,7 @@ invalid_group_rule(Parser *p)
return _res;
}

// invalid_import_from_targets: import_from_as_names ','
// invalid_import_from_targets: import_from_as_names ',' NEWLINE
static void *
invalid_import_from_targets_rule(Parser *p)
{
Expand All @@ -19551,21 +19551,24 @@ invalid_import_from_targets_rule(Parser *p)
}
void * _res = NULL;
int _mark = p->mark;
{ // import_from_as_names ','
{ // import_from_as_names ',' NEWLINE
if (p->error_indicator) {
D(p->level--);
return NULL;
}
D(fprintf(stderr, "%*c> invalid_import_from_targets[%d-%d]: %s\n", p->level, ' ', _mark, p->mark, "import_from_as_names ','"));
D(fprintf(stderr, "%*c> invalid_import_from_targets[%d-%d]: %s\n", p->level, ' ', _mark, p->mark, "import_from_as_names ',' NEWLINE"));
Token * _literal;
asdl_alias_seq* import_from_as_names_var;
Token * newline_var;
if (
(import_from_as_names_var = import_from_as_names_rule(p)) // import_from_as_names
&&
(_literal = _PyPegen_expect_token(p, 12)) // token=','
&&
(newline_var = _PyPegen_expect_token(p, NEWLINE)) // token='NEWLINE'
)
{
D(fprintf(stderr, "%*c+ invalid_import_from_targets[%d-%d]: %s succeeded!\n", p->level, ' ', _mark, p->mark, "import_from_as_names ','"));
D(fprintf(stderr, "%*c+ invalid_import_from_targets[%d-%d]: %s succeeded!\n", p->level, ' ', _mark, p->mark, "import_from_as_names ',' NEWLINE"));
_res = RAISE_SYNTAX_ERROR ( "trailing comma not allowed without surrounding parentheses" );
if (_res == NULL && PyErr_Occurred()) {
p->error_indicator = 1;
Expand All @@ -19576,7 +19579,7 @@ invalid_import_from_targets_rule(Parser *p)
}
p->mark = _mark;
D(fprintf(stderr, "%*c%s invalid_import_from_targets[%d-%d]: %s failed!\n", p->level, ' ',
p->error_indicator ? "ERROR!" : "-", _mark, p->mark, "import_from_as_names ','"));
p->error_indicator ? "ERROR!" : "-", _mark, p->mark, "import_from_as_names ',' NEWLINE"));
}
_res = NULL;
done:
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