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gh-138294: Fix Misleading error for ((a) := 1) #138627

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gh-138294: Fix Misleading error for ((a) := 1) #138627

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185ce34
Raise error for parenthesized target in walrus expression
Devansh-b Sep 7, 2025
d9c911e
Raise SyntaxError for parenthesized walrus target (#138294)
Devansh-b Sep 7, 2025
bb95d1f
Update Misc/NEWS.d/next/Core_and_Builtins/2025-09-08-12-30-00.gh-issu…
dbXD320 Sep 7, 2025
84fbba0
Add test for parenthesized walrus target
Devansh-b Sep 8, 2025
7eb3d1e
Move parenthesized walrus target test to docstring in test_syntax
Devansh-b Sep 9, 2025
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3 changes: 3 additions & 0 deletions Grammar/python.gram
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Original file line number Diff line number Diff line change
Expand Up @@ -1261,6 +1261,9 @@ invalid_expression:
RAISE_SYNTAX_ERROR_KNOWN_RANGE(a, b, "t-string: lambda expressions are not allowed without parentheses") }

invalid_named_expression(memo):
| '(' a=NAME ')' ':=' expression {
RAISE_SYNTAX_ERROR_KNOWN_LOCATION(
a, "cannot parenthesize target name in assignment expression") }
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| a=expression ':=' expression {
RAISE_SYNTAX_ERROR_KNOWN_LOCATION(
a, "cannot use assignment expressions with %s", _PyPegen_get_expr_name(a)) }
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5 changes: 5 additions & 0 deletions Lib/test/test_syntax.py
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Expand Up @@ -2852,6 +2852,11 @@ def test_assign_del(self):
# report "cannot delete name"
self._check_error("del a += b", "invalid syntax")

def test_parenthesized_named_expression_target(self):
self._check_error(
"((a) := 1)",
"cannot parenthesize target name in assignment expression")

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@lysnikolaou lysnikolaou Sep 8, 2025

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I think it'd be best if this went in the docstring at the top of the file instead of a separate test. It can probably go at the very bottom of that docstring with a short description of the error being tested, something along the lines of Invalid parenthesization inside assignment expressions.

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@pablogsal pablogsal Sep 8, 2025

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@dbXD320 You can add a new section like this:

cpython/Lib/test/test_syntax.py

Line 2471 in 921f61b

Invalid expressions in type scopes:

def test_global_param_err_first(self):
source = """if 1:
def error(a):
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1 change: 1 addition & 0 deletions Misc/NEWS.d/next/Core_and_Builtins/2025-09-08-12-30-00.gh-issue-138294.abcd12.rst
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@@ -0,0 +1 @@
Raise an improved :exc:`SyntaxError` when using parentheses around a walrus target.
37 changes: 37 additions & 0 deletions Parser/parser.c
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