[3.14] gh-134759: fix UnboundLocalError in email.message.Message.get_payload (GH-136071) (#136579)

gh-134759: fix `UnboundLocalError` in `email.message.Message.get_payload` (GH-136071)
(cherry picked from commit 25335d297b)

Co-authored-by: Kliment Lamonov <klimentlamonov@yandex.ru>
Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>

Lib/email/message.py

@@ -313,6 +313,8 @@ class Message:
                 # If it does happen, turn the string into bytes in a way
                 # guaranteed not to fail.
                 bpayload = payload.encode('raw-unicode-escape')
+        else:
+            bpayload = payload
         if cte == 'quoted-printable':
             return quopri.decodestring(bpayload)
         elif cte == 'base64':

Lib/test/test_email/test_message.py

@@ -1055,6 +1055,15 @@ class TestEmailMessage(TestEmailMessageBase, TestEmailBase):
         # AttributeError: 'str' object has no attribute 'is_attachment'
         m.get_body()
 
+    def test_get_bytes_payload_with_quoted_printable_encoding(self):
+        # We use a memoryview to avoid directly changing the private payload
+        # and to prevent using the dedicated paths for string or bytes objects.
+        payload = memoryview(b'Some payload')
+        m = self._make_message()
+        m.add_header('Content-Transfer-Encoding', 'quoted-printable')
+        m.set_payload(payload)
+        self.assertEqual(m.get_payload(decode=True), payload)
+
 
 class TestMIMEPart(TestEmailMessageBase, TestEmailBase):
     # Doing the full test run here may seem a bit redundant, since the two

Misc/ACKS

@@ -1054,6 +1054,7 @@ Alexander Lakeev
 David Lam
 Thomas Lamb
 Valerie Lambert
+Kliment Lamonov
 Peter Lamut
 Jean-Baptiste "Jiba" Lamy
 Ronan Lamy

Misc/NEWS.d/next/Library/2025-06-28-11-32-57.gh-issue-134759.AjjKcG.rst

@@ -0,0 +1,2 @@
+Fix :exc:`UnboundLocalError` in :func:`email.message.Message.get_payload` when
+the payload to decode is a :class:`bytes` object. Patch by Kliment Lamonov.