From 0db3d0892e2c3a54ea5927bdeb97f1dcc03166d1 Mon Sep 17 00:00:00 2001
From: Pablo Galindo Salgado <Pablogsal@gmail.com>
Date: Sun, 3 Aug 2025 17:10:51 +0100
Subject: [PATCH 1/2] gh-137314: Fix incorrect treatment of format specs in raw
 fstrings (GH-137328) (cherry picked from commit
 0153d82a5ab0c6ac16c046bdd4438ea11b58d59d)

Co-authored-by: Pablo Galindo Salgado <Pablogsal@gmail.com>
---
 Lib/test/test_fstring.py                      | 28 +++++++++++++++++++
 ...-08-02-23-04-57.gh-issue-137314.wjEdzD.rst |  5 ++++
 Parser/action_helpers.c                       | 10 ++++++-
 3 files changed, 42 insertions(+), 1 deletion(-)
 create mode 100644 Misc/NEWS.d/next/Core_and_Builtins/2025-08-02-23-04-57.gh-issue-137314.wjEdzD.rst

diff --git a/Lib/test/test_fstring.py b/Lib/test/test_fstring.py
index c2ab603a8a775c..5e743d34d2a573 100644
--- a/Lib/test/test_fstring.py
+++ b/Lib/test/test_fstring.py
@@ -1821,6 +1821,34 @@ def test_newlines_in_format_specifiers(self):
         for case in valid_cases:
             compile(case, "<string>", "exec")
 
+    def test_raw_fstring_format_spec(self):
+        # Test raw f-string format spec behavior (Issue #137314).
+        #
+        # Raw f-strings should preserve literal backslashes in format specifications,
+        # not interpret them as escape sequences.
+        class UnchangedFormat:
+            """Test helper that returns the format spec unchanged."""
+            def __format__(self, format):
+                return format
+
+        # Test basic escape sequences
+        self.assertEqual(f"{UnchangedFormat():\xFF}", 'ÿ')
+        self.assertEqual(rf"{UnchangedFormat():\xFF}", '\\xFF')
+
+        # Test nested expressions with raw/non-raw combinations
+        self.assertEqual(rf"{UnchangedFormat():{'\xFF'}}", 'ÿ')
+        self.assertEqual(f"{UnchangedFormat():{r'\xFF'}}", '\\xFF')
+        self.assertEqual(rf"{UnchangedFormat():{r'\xFF'}}", '\\xFF')
+
+        # Test continuation character in format specs
+        self.assertEqual(f"""{UnchangedFormat():{'a'\
+                        'b'}}""", 'ab')
+        self.assertEqual(rf"""{UnchangedFormat():{'a'\
+                         'b'}}""", 'ab')
+
+        # Test multiple format specs in same raw f-string
+        self.assertEqual(rf"{UnchangedFormat():\xFF} {UnchangedFormat():\n}", '\\xFF \\n')
+
 
 if __name__ == '__main__':
     unittest.main()
diff --git a/Misc/NEWS.d/next/Core_and_Builtins/2025-08-02-23-04-57.gh-issue-137314.wjEdzD.rst b/Misc/NEWS.d/next/Core_and_Builtins/2025-08-02-23-04-57.gh-issue-137314.wjEdzD.rst
new file mode 100644
index 00000000000000..09d0c3e68fc1ed
--- /dev/null
+++ b/Misc/NEWS.d/next/Core_and_Builtins/2025-08-02-23-04-57.gh-issue-137314.wjEdzD.rst
@@ -0,0 +1,5 @@
+Fixed a regression where raw f-strings incorrectly interpreted
+escape sequences in format specifications. Raw f-strings now properly preserve
+literal backslashes in format specs, matching the behavior from Python 3.11.
+For example, ``rf"{obj:\xFF}"`` now correctly produces ``'\\xFF'`` instead of
+``'ÿ'``. Patch by Pablo Galindo.
diff --git a/Parser/action_helpers.c b/Parser/action_helpers.c
index 99dd0976c6137d..6a8aa4ef044f8e 100644
--- a/Parser/action_helpers.c
+++ b/Parser/action_helpers.c
@@ -1369,7 +1369,15 @@ expr_ty _PyPegen_decoded_constant_from_token(Parser* p, Token* tok) {
     if (PyBytes_AsStringAndSize(tok->bytes, &bstr, &bsize) == -1) {
         return NULL;
     }
-    PyObject* str = _PyPegen_decode_string(p, 0, bstr, bsize, tok);
+
+    // Check if we're inside a raw f-string for format spec decoding
+    int is_raw = 0;
+    if (INSIDE_FSTRING(p->tok)) {
+        tokenizer_mode *mode = TOK_GET_MODE(p->tok);
+        is_raw = mode->raw;
+    }
+
+    PyObject* str = _PyPegen_decode_string(p, is_raw, bstr, bsize, tok);
     if (str == NULL) {
         return NULL;
     }

From f0e342304b6ce6a29e2d03d8ca73081957166bde Mon Sep 17 00:00:00 2001
From: Pablo Galindo <pablogsal@gmail.com>
Date: Sun, 3 Aug 2025 17:35:45 +0100
Subject: [PATCH 2/2] fixup! gh-137314: Fix incorrect treatment of format specs
 in raw fstrings (GH-137328) (cherry picked from commit
 0153d82a5ab0c6ac16c046bdd4438ea11b58d59d)

---
 Parser/action_helpers.c |  3 ++-
 Parser/lexer/lexer.c    | 16 ----------------
 Parser/lexer/state.h    | 16 ++++++++++++++++
 3 files changed, 18 insertions(+), 17 deletions(-)

diff --git a/Parser/action_helpers.c b/Parser/action_helpers.c
index 6a8aa4ef044f8e..6f841ef2e4f9c3 100644
--- a/Parser/action_helpers.c
+++ b/Parser/action_helpers.c
@@ -1,6 +1,7 @@
 #include <Python.h>
 
 #include "pegen.h"
+#include "lexer/state.h"
 #include "string_parser.h"
 #include "pycore_runtime.h"         // _PyRuntime
 #include "pycore_pystate.h"         // _PyInterpreterState_GET()
@@ -1374,7 +1375,7 @@ expr_ty _PyPegen_decoded_constant_from_token(Parser* p, Token* tok) {
     int is_raw = 0;
     if (INSIDE_FSTRING(p->tok)) {
         tokenizer_mode *mode = TOK_GET_MODE(p->tok);
-        is_raw = mode->raw;
+        is_raw = mode->f_string_raw;
     }
 
     PyObject* str = _PyPegen_decode_string(p, is_raw, bstr, bsize, tok);
diff --git a/Parser/lexer/lexer.c b/Parser/lexer/lexer.c
index d29b0bbd25d2ab..384239bd414c38 100644
--- a/Parser/lexer/lexer.c
+++ b/Parser/lexer/lexer.c
@@ -22,22 +22,6 @@
                || c == '_'\
                || (c >= 128))
 
-#ifdef Py_DEBUG
-static inline tokenizer_mode* TOK_GET_MODE(struct tok_state* tok) {
-    assert(tok->tok_mode_stack_index >= 0);
-    assert(tok->tok_mode_stack_index < MAXFSTRINGLEVEL);
-    return &(tok->tok_mode_stack[tok->tok_mode_stack_index]);
-}
-static inline tokenizer_mode* TOK_NEXT_MODE(struct tok_state* tok) {
-    assert(tok->tok_mode_stack_index >= 0);
-    assert(tok->tok_mode_stack_index + 1 < MAXFSTRINGLEVEL);
-    return &(tok->tok_mode_stack[++tok->tok_mode_stack_index]);
-}
-#else
-#define TOK_GET_MODE(tok) (&(tok->tok_mode_stack[tok->tok_mode_stack_index]))
-#define TOK_NEXT_MODE(tok) (&(tok->tok_mode_stack[++tok->tok_mode_stack_index]))
-#endif
-
 #define MAKE_TOKEN(token_type) _PyLexer_token_setup(tok, token, token_type, p_start, p_end)
 #define MAKE_TYPE_COMMENT_TOKEN(token_type, col_offset, end_col_offset) (\
                 _PyLexer_type_comment_token_setup(tok, token, token_type, col_offset, end_col_offset, p_start, p_end))
diff --git a/Parser/lexer/state.h b/Parser/lexer/state.h
index 9ed3babfdbfbf1..d8791d89dd02db 100644
--- a/Parser/lexer/state.h
+++ b/Parser/lexer/state.h
@@ -1,6 +1,7 @@
 #ifndef _PY_LEXER_H_
 #define _PY_LEXER_H_
 
+#include "Python.h"
 #include "object.h"
 
 #define MAXINDENT 100       /* Max indentation level */
@@ -138,5 +139,20 @@ void _PyTokenizer_Free(struct tok_state *);
 void _PyToken_Free(struct token *);
 void _PyToken_Init(struct token *);
 
+#ifdef Py_DEBUG
+static inline tokenizer_mode* TOK_GET_MODE(struct tok_state* tok) {
+    assert(tok->tok_mode_stack_index >= 0);
+    assert(tok->tok_mode_stack_index < MAXFSTRINGLEVEL);
+    return &(tok->tok_mode_stack[tok->tok_mode_stack_index]);
+}
+static inline tokenizer_mode* TOK_NEXT_MODE(struct tok_state* tok) {
+    assert(tok->tok_mode_stack_index >= 0);
+    assert(tok->tok_mode_stack_index + 1 < MAXFSTRINGLEVEL);
+    return &(tok->tok_mode_stack[++tok->tok_mode_stack_index]);
+}
+#else
+#define TOK_GET_MODE(tok) (&(tok->tok_mode_stack[tok->tok_mode_stack_index]))
+#define TOK_NEXT_MODE(tok) (&(tok->tok_mode_stack[++tok->tok_mode_stack_index]))
+#endif
 
 #endif

<!DOCTYPE html PUBLIC '-//W3C//DTD XHTML 1.0 Transitional//EN' 'http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd'>
<html xmlns='http://www.w3.org/1999/xhtml'>
<head>
<title>pFad - Phonifier reborn</title>
<meta http-equiv='Content-Type' content='text/html; charset=utf-8' />
</head>
<body>
<h1>Pfad - The Proxy pFad of &#169; 2024 Garber Painting. All rights reserved.</h1>


<!-- Disclaimer -->
<p>Note: This service is not intended for secure transactions such as banking, social media, email, or purchasing. Use at your own risk. We assume no liability whatsoever for broken pages.</p>
<br>
<p>Alternative Proxies:</p><p><a href="http://rainy.clevelandohioweatherforecast.com/php-proxy/index.php?q=https://patch-diff.githubusercontent.com/raw/python/cpython/pull/137345.patch" target="_blank">Alternative Proxy</a></p><p><a href="http://rainy.clevelandohioweatherforecast.com/pFad/index.php?u=https://patch-diff.githubusercontent.com/raw/python/cpython/pull/137345.patch" target="_blank">pFad Proxy</a></p><p><a href="http://rainy.clevelandohioweatherforecast.com/pFad/v3index.php?u=https://patch-diff.githubusercontent.com/raw/python/cpython/pull/137345.patch" target="_blank">pFad v3 Proxy</a></p><p><a href="http://rainy.clevelandohioweatherforecast.com/pFad/v4index.php?u=https://patch-diff.githubusercontent.com/raw/python/cpython/pull/137345.patch" target="_blank">pFad v4 Proxy</a></p></body>
</html>