Fixed #35648 -- Raised NotImplementedError in SafeString.__add__ for non-string RHS.

This change ensures SafeString addition operations handle non-string RHS
properly, allowing them to implement __radd__ for better compatibility.

1 files changed, 10 insertions, 4 deletions

diff --git a/django/utils/safestring.py b/django/utils/safestring.py
index 4eb0207a66..1ac9b877e9 100644
--- a/django/utils/safestring.py
+++ b/django/utils/safestring.py
@@ -35,10 +35,16 @@ class SafeString(str, SafeData):
         Concatenating a safe string with another safe bytestring or
         safe string is safe. Otherwise, the result is no longer safe.
         """
-        t = super().__add__(rhs)
-        if isinstance(rhs, SafeData):
-            return SafeString(t)
-        return t
+        if isinstance(rhs, str):
+            t = super().__add__(rhs)
+            if isinstance(rhs, SafeData):
+                t = SafeString(t)
+            return t
+
+        # Give the rhs object a chance to handle the addition, for example if
+        # the rhs object's class implements `__radd__`. More details:
+        # https://docs.python.org/3/reference/datamodel.html#object.__radd__
+        return NotImplemented
 
     def __str__(self):
         return self