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gh-145241: specialize SyntaxError for single trailing-comma with item #145282

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gh-145241: specialize SyntaxError for single trailing-comma with item #145282

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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 @@ -1447,6 +1447,8 @@ invalid_import_from_targets:
RAISE_SYNTAX_ERROR_STARTING_FROM(token, "Expected one or more names after 'import'") }

invalid_with_stmt:
| ['async'] 'with' expression ['as' star_target] ',' ':' {
RAISE_SYNTAX_ERROR("single 'with' item has a trailing comma") }
Comment on lines +1450 to +1451
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@johnslavik johnslavik Feb 26, 2026 •
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Covers multiple items case and moves the indicator to the trailing comma. This is a suggestion block, so need to regen pegen.

Suggested change
| ['async'] 'with' expression ['as' star_target] ',' ':' {
RAISE_SYNTAX_ERROR("single 'with' item has a trailing comma") }
| ['async'] 'with' ','.(expression ['as' star_target])+ trailing=',' ':' {
RAISE_SYNTAX_ERROR_KNOWN_LOCATION(trailing, "the last 'with' item has a trailing comma") }

| ['async'] 'with' ','.(expression ['as' star_target])+ NEWLINE { RAISE_SYNTAX_ERROR("expected ':'") }
| ['async'] 'with' '(' ','.(expressions ['as' star_target])+ ','? ')' NEWLINE { RAISE_SYNTAX_ERROR("expected ':'") }
invalid_with_stmt_indent:
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8 changes: 8 additions & 0 deletions Lib/test/test_syntax.py
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Expand Up @@ -2061,6 +2061,14 @@
Traceback (most recent call last):
SyntaxError: trailing comma not allowed without surrounding parentheses
>>> with item,: pass
Traceback (most recent call last):
SyntaxError: single 'with' item has a trailing comma
>>> with item as x,: pass
Traceback (most recent call last):
SyntaxError: single 'with' item has a trailing comma
Comment on lines +2064 to +2071
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@johnslavik johnslavik Feb 26, 2026 •
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Covers multiple items cases.

Suggested change
>>> with item,: pass
Traceback (most recent call last):
SyntaxError: single 'with' item has a trailing comma
>>> with item as x,: pass
Traceback (most recent call last):
SyntaxError: single 'with' item has a trailing comma
>>> with item,: pass
Traceback (most recent call last):
SyntaxError: the last 'with' item has a trailing comma
>>> with item as x,: pass
Traceback (most recent call last):
SyntaxError: the last 'with' item has a trailing comma
>>> with item1, item2,: pass
Traceback (most recent call last):
SyntaxError: the last 'with' item has a trailing comma
>>> with item1 as x, item2,: pass
Traceback (most recent call last):
SyntaxError: the last 'with' item has a trailing comma
>>> with item1 as x, item2 as y,: pass
Traceback (most recent call last):
SyntaxError: the last 'with' item has a trailing comma
>>> with item1, item2 as y,: pass
Traceback (most recent call last):
SyntaxError: the last 'with' item has a trailing comma

>>> import a from b
Traceback (most recent call last):
SyntaxError: Did you mean to use 'from ... import ...' instead?
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3 changes: 3 additions & 0 deletions Misc/NEWS.d/next/Core_and_Builtins/2026-02-26-18-00-00.gh-issue-145241.hL2k9Q.rst
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@@ -0,0 +1,3 @@
Specialized the parser error for a single unparenthesized ``with`` item followed
by a trailing comma (for example, ``with item,:``), raising a clearer
:exc:`SyntaxError` message. Patch by Pablo Galindo.
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