#11558: Better message if attach called on non-multipart.

Original patch by Varun Sharma.

1 files changed, 5 insertions, 1 deletions

diff --git a/Lib/email/message.py b/Lib/email/message.py
index 88b5fa3552..b4bc8cbc9e 100644
--- a/Lib/email/message.py
+++ b/Lib/email/message.py
@@ -203,7 +203,11 @@ class Message:
         if self._payload is None:
             self._payload = [payload]
         else:
-            self._payload.append(payload)
+            try:
+                self._payload.append(payload)
+            except AttributeError:
+                raise TypeError("Attach is not valid on a message with a"
+                                " non-multipart payload")
 
     def get_payload(self, i=None, decode=False):
         """Return a reference to the payload.