[Python-checkins] [3.13] gh-130618: Fix parser error when using lambdas inside f-strings (GH-130638) (#130642)

[pablogsal]

https://github.com/python/cpython/commit/2d7145decb1acad4636a21b77ab3a9c4f48af36d
commit: 2d7145decb1acad4636a21b77ab3a9c4f48af36d
branch: 3.13
author: Pablo Galindo Salgado <pablog...@gmail.com>
committer: pablogsal <pablog...@gmail.com>
date: 2025-03-01T18:10:03Z
summary:

[3.13] gh-130618: Fix parser error when using lambdas inside f-strings 
(GH-130638) (#130642)

(cherry picked from commit e06bebb87e1b33f7251196e1ddb566f528c3fc98)

Signed-off-by: Pablo Galindo <pablog...@gmail.com>

files:
A 
Misc/NEWS.d/next/Core_and_Builtins/2025-02-27-15-07-06.gh-issue-130618.JTcsRB.rst
M Lib/test/test_grammar.py
M Parser/lexer/lexer.c

diff --git a/Lib/test/test_grammar.py b/Lib/test/test_grammar.py
index c72f4387108ca8..46eb5736fe3a89 100644
--- a/Lib/test/test_grammar.py
+++ b/Lib/test/test_grammar.py
@@ -2030,6 +2030,18 @@ async def foo():
         with self.assertRaises(Done):
             foo().send(None)
 
+    def test_complex_lambda(self):
+        def test1(foo, bar):
+            return ""
+
+        def test2():
+            return f"{test1(
+                foo=lambda: '、、、、、、、、、、、、、、、、、',
+                bar=lambda: 'abcdefghijklmnopqrstuvwxyz 123456789 123456789',
+            )}"
+
+        self.assertEqual(test2(), "")
+
 
 if __name__ == '__main__':
     unittest.main()
diff --git 
a/Misc/NEWS.d/next/Core_and_Builtins/2025-02-27-15-07-06.gh-issue-130618.JTcsRB.rst
 
b/Misc/NEWS.d/next/Core_and_Builtins/2025-02-27-15-07-06.gh-issue-130618.JTcsRB.rst
new file mode 100644
index 00000000000000..de67496108e2a7
--- /dev/null
+++ 
b/Misc/NEWS.d/next/Core_and_Builtins/2025-02-27-15-07-06.gh-issue-130618.JTcsRB.rst
@@ -0,0 +1,3 @@
+Fix a bug that was causing ``UnicodeDecodeError`` or ``SystemError`` to be
+raised when using f-strings with ``lambda`` expressions with non-ASCII
+characters. Patch by Pablo Galindo
diff --git a/Parser/lexer/lexer.c b/Parser/lexer/lexer.c
index 3ced1be0b003b8..15e6332ee35718 100644
--- a/Parser/lexer/lexer.c
+++ b/Parser/lexer/lexer.c
@@ -211,9 +211,13 @@ _PyLexer_update_fstring_expr(struct tok_state *tok, char 
cur)
             break;
         case '}':
         case '!':
-        case ':':
             tok_mode->last_expr_end = strlen(tok->start);
             break;
+        case ':':
+            if (tok_mode->last_expr_end == -1) {
+               tok_mode->last_expr_end = strlen(tok->start);
+            }
+            break;
         default:
             Py_UNREACHABLE();
     }

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