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gh-146260: Improve syntax error for assignment expression inside conditional expression #146305

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gh-146260: Improve syntax error for assignment expression inside conditional expression #146305

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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 @@ -1264,6 +1264,8 @@ invalid_expression:
# Soft keywords need to also be ignored because they can be parsed as NAME NAME
| !(NAME STRING | SOFT_KEYWORD) a=disjunction b=expression_without_invalid {
_PyPegen_raise_error_for_missing_comma(p, a, b) }
| disjunction 'if' a=disjunction ':=' b=disjunction {
RAISE_SYNTAX_ERROR_KNOWN_RANGE(a, b, "assignment expression must be parenthesized inside conditional expression" ) }
| a=disjunction 'if' b=disjunction !('else'|':') { RAISE_SYNTAX_ERROR_KNOWN_RANGE(a, b, "expected 'else' after 'if' expression") }
| a=disjunction 'if' b=disjunction 'else' !expression {
RAISE_SYNTAX_ERROR_ON_NEXT_TOKEN("expected expression after 'else', but statement is given") }
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4 changes: 4 additions & 0 deletions Lib/test/test_syntax.py
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Expand Up @@ -180,6 +180,10 @@
Traceback (most recent call last):
SyntaxError: expected expression before 'if', but statement is given

>>> 1 if x := True else 2
Traceback (most recent call last):
SyntaxError: assignment expression must be parenthesized inside conditional expression

>>> if True:
... print("Hello"
...
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3 changes: 3 additions & 0 deletions Misc/NEWS.d/next/Core_and_Builtins/2026-03-22-14-49-48.gh-issue-146260.s8PzJW.rst
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@@ -0,0 +1,3 @@
Improve :exc:`SyntaxError` message when an :ref:`assignment expression
<assignment-expressions>` is used inside the ``if`` clause of a
:ref:`conditional expression <if_expr>`. Patch by Brian Schubert.
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