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gh-138716: Fix assert a := b syntax error message #138718

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Merged
sobolevn merged 1 commit into from
Sep 10, 2025
Merged

gh-138716: Fix assert a := b syntax error message #138718

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gh-138716: Fix assert a := b syntax error message
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@sobolevn
sobolevn committed Sep 10, 2025
commit 9bc06a651fe630f11bf6cc1cfddc39649d310dbb
8 changes: 8 additions & 0 deletions Grammar/python.gram
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Original file line number Diff line number Diff line change
Expand Up @@ -1315,6 +1315,14 @@ invalid_assert_stmt:
a, b,
"cannot assign to %s here. Maybe you meant '==' instead of '='?",
_PyPegen_get_expr_name(a)) }
| 'assert' a=expression ':=' b=expression {
RAISE_SYNTAX_ERROR_KNOWN_RANGE(
a, b,
"cannot use named expression without parentheses here") }
| 'assert' expression ',' a=expression ':=' b=expression {
RAISE_SYNTAX_ERROR_KNOWN_RANGE(
a, b,
"cannot use named expression without parentheses here") }
invalid_block:
| NEWLINE !INDENT { RAISE_INDENTATION_ERROR("expected an indented block") }
invalid_comprehension:
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9 changes: 7 additions & 2 deletions Lib/test/test_syntax.py
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Expand Up @@ -2690,10 +2690,15 @@ def f(x: *b)
Asserts:

>>> assert (a := 1) # ok
>>> # TODO(@sobolevn): improve this message in the next PR
>>> assert 1, (a := 1) # ok

>>> assert a := 1
Traceback (most recent call last):
SyntaxError: invalid syntax
SyntaxError: cannot use named expression without parentheses here

>>> assert 1, a := 1
Traceback (most recent call last):
SyntaxError: cannot use named expression without parentheses here

>>> assert 1 = 2 = 3
Traceback (most recent call last):
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2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Core_and_Builtins/2025-09-09-23-59-13.gh-issue-138716.UawDY0.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,2 @@
Improve :exc:`SyntaxError` message for :keyword:`assert` in cases like
``assert a := b``.
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