[3.13] gh-130618: Fix parser error when using lambdas inside f-strings (

GH-130638) (cherry picked from commit e06bebb) Co-authored-by: Pablo Galindo Salgado <[email protected]> Signed-off-by: Pablo Galindo <[email protected]>
python · pablogsal · Mar 1, 2025 · Feb 27, 2025 · Feb 27, 2025 · 91ab8b26d9c366b065ff7864f05e4b4c3c356f0e
commit 91ab8b26d9c366b065ff7864f05e4b4c3c356f0e
diff --git 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
@@ -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
@@ -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();
     }