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gh-137786: fix error msg for *args, **kwargs default value #137793

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gh-137786: fix error msg for *args, **kwargs default value #137793

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233b9a6
fix: error msg for *args, **kwargs default value
Aug 15, 2025
98cbe83
fix: add explanation without modifying the original message
Aug 15, 2025
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8 changes: 4 additions & 4 deletions Grammar/python.gram
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Original file line number Diff line number Diff line change
Expand Up @@ -1331,11 +1331,11 @@ invalid_default:
invalid_star_etc:
| a='*' (')' | ',' (')' | '**')) { RAISE_SYNTAX_ERROR_KNOWN_LOCATION(a, "named parameters must follow bare *") }
| '*' ',' TYPE_COMMENT { RAISE_SYNTAX_ERROR("bare * has associated type comment") }
| '*' param a='=' { RAISE_SYNTAX_ERROR_KNOWN_LOCATION(a, "var-positional parameter cannot have default value") }
| '*' param a='=' { RAISE_SYNTAX_ERROR_KNOWN_LOCATION(a, "var-positional parameter cannot have default value, pass values explicitly") }
| '*' (param_no_default | ',') param_maybe_default* a='*' (param_no_default | ',') {
RAISE_SYNTAX_ERROR_KNOWN_LOCATION(a, "* may appear only once") }
invalid_kwds:
| '**' param a='=' { RAISE_SYNTAX_ERROR_KNOWN_LOCATION(a, "var-keyword parameter cannot have default value") }
| '**' param a='=' { RAISE_SYNTAX_ERROR_KNOWN_LOCATION(a, "var-keyword parameter cannot have default value, pass values explicitly") }
| '**' param ',' a=param { RAISE_SYNTAX_ERROR_KNOWN_LOCATION(a, "parameters cannot follow var-keyword parameter") }
| '**' param ',' a[Token*]=('*'|'**'|'/') { RAISE_SYNTAX_ERROR_KNOWN_LOCATION(a, "parameters cannot follow var-keyword parameter") }
invalid_parameters_helper: # This is only there to avoid type errors
Expand All @@ -1359,11 +1359,11 @@ invalid_lambda_parameters_helper:
| lambda_param_with_default+
invalid_lambda_star_etc:
| '*' (':' | ',' (':' | '**')) { RAISE_SYNTAX_ERROR("named parameters must follow bare *") }
| '*' lambda_param a='=' { RAISE_SYNTAX_ERROR_KNOWN_LOCATION(a, "var-positional parameter cannot have default value") }
| '*' lambda_param a='=' { RAISE_SYNTAX_ERROR_KNOWN_LOCATION(a, "var-positional parameter cannot have default value, pass values explicitly") }
| '*' (lambda_param_no_default | ',') lambda_param_maybe_default* a='*' (lambda_param_no_default | ',') {
RAISE_SYNTAX_ERROR_KNOWN_LOCATION(a, "* may appear only once") }
invalid_lambda_kwds:
| '**' lambda_param a='=' { RAISE_SYNTAX_ERROR_KNOWN_LOCATION(a, "var-keyword parameter cannot have default value") }
| '**' lambda_param a='=' { RAISE_SYNTAX_ERROR_KNOWN_LOCATION(a, "var-keyword parameter cannot have default value, pass values explicitly") }
| '**' lambda_param ',' a=lambda_param { RAISE_SYNTAX_ERROR_KNOWN_LOCATION(a, "parameters cannot follow var-keyword parameter") }
| '**' lambda_param ',' a[Token*]=('*'|'**'|'/') { RAISE_SYNTAX_ERROR_KNOWN_LOCATION(a, "parameters cannot follow var-keyword parameter") }
invalid_double_type_comments:
Expand Down
12 changes: 6 additions & 6 deletions Lib/test/test_syntax.py
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Expand Up @@ -461,22 +461,22 @@
>>> def foo(a,*b=3,c):
... pass
Traceback (most recent call last):
SyntaxError: var-positional parameter cannot have default value
SyntaxError: var-positional parameter cannot have default value, pass values explicitly

>>> def foo(a,*b: int=,c):
... pass
Traceback (most recent call last):
SyntaxError: var-positional parameter cannot have default value
SyntaxError: var-positional parameter cannot have default value, pass values explicitly

>>> def foo(a,**b=3):
... pass
Traceback (most recent call last):
SyntaxError: var-keyword parameter cannot have default value
SyntaxError: var-keyword parameter cannot have default value, pass values explicitly

>>> def foo(a,**b: int=3):
... pass
Traceback (most recent call last):
SyntaxError: var-keyword parameter cannot have default value
SyntaxError: var-keyword parameter cannot have default value, pass values explicitly

>>> def foo(a,*a, b, **c, d):
... pass
Expand Down Expand Up @@ -577,11 +577,11 @@

>>> lambda a,*b=3,c: None
Traceback (most recent call last):
SyntaxError: var-positional parameter cannot have default value
SyntaxError: var-positional parameter cannot have default value, pass values explicitly

>>> lambda a,**b=3: None
Traceback (most recent call last):
SyntaxError: var-keyword parameter cannot have default value
SyntaxError: var-keyword parameter cannot have default value, pass values explicitly

>>> lambda a, *a, b, **c, d: None
Traceback (most recent call last):
Expand Down
2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Core_and_Builtins/2025-08-15-12-31-45.gh-issue-137786.HkKBqf.rst
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@@ -0,0 +1,2 @@
fix error msg for *args, **kwargs default value
Yoonho Hann.
8 changes: 4 additions & 4 deletions Parser/parser.c
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