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[3.13] gh-154711: Strip comments after escaped quotes in f-string debug text #154914

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[3.13] gh-154711: Strip comments after escaped quotes in f-string debug text #154914

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5 changes: 5 additions & 0 deletions Lib/test/test_fstring.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1664,6 +1664,11 @@ def __repr__(self):
self.assertEqual(f'{" # nooo "=}', '" # nooo "=\' # nooo \'')
self.assertEqual(f'{" \" # nooo \" "=}', '" \\" # nooo \\" "=\' " # nooo " \'')

# A real comment after a string that ends with an escaped quote must
# still be stripped (gh-154711).
self.assertEqual(f"{'\'' = # comment
}", "'\\'' = \n" + repr("'"))

self.assertEqual(f'{ # some comment goes here
"""hello"""=}', ' \n """hello"""=\'hello\'')
self.assertEqual(f'{"""# this is not a comment
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3 changes: 3 additions & 0 deletions Misc/NEWS.d/next/Core_and_Builtins/2026-07-30-14-40-00.gh-issue-154711.nUxYXc.rst
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@@ -0,0 +1,3 @@
Fix a bug where a comment placed after a string that ends with an escaped

@pablogsal pablogsal Aug 10, 2026

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This goes back to 3.12 (gh-112243) and the same code is still in 3.13 and 3.14, so we want the backport labels here, no?

@ArneshBanerjee ArneshBanerjee Aug 10, 2026

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Confirmed, the same escape-skip bug is present in 3.12 (tokenizer.c) and 3.13 (lexer.c) as well. Happy to have backport labels added.

quote could leak into the output of a debug f-string. Now the comment is
stripped as expected.
13 changes: 13 additions & 0 deletions Parser/lexer/lexer.c
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Expand Up @@ -162,6 +162,19 @@ set_fstring_expr(struct tok_state* tok, struct token *token, char c) {
while (i < expression_size) {
char ch = expression[i];

// Copy escaped characters as-is. This keeps an escaped quote from
// flipping the in_string state, which would otherwise stop a real
// comment from being detected (see the detection loop above).
if (ch == '\\') {
result[j++] = ch;
i++;
if (i < expression_size) {
result[j++] = expression[i];
i++;
}
continue;
}

// Handle string quotes
if (ch == '"' || ch == '\'') {
// See comment above to understand this part
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