gh-151769: Fix IPv6Address ordering to account for scope_id

Author: factnn

Lib/ipaddress.py

@@ -2002,6 +2002,21 @@ def __str__(self):
     def __hash__(self):
         return hash((self._ip, self._scope_id))
 
+    def __lt__(self, other):
+        if not isinstance(other, IPv6Address):
+            return NotImplemented
+        if self._ip != other._ip:
+            return self._ip < other._ip
+        self_scope = self._scope_id
+        other_scope = other._scope_id
+        if self_scope is None and other_scope is None:
+            return False
+        if other_scope is None:
+            return False
+        if self_scope is None:
+            return True
+        return self_scope < other_scope
+
     def __eq__(self, other):
         address_equal = super().__eq__(other)
         if address_equal is NotImplemented:

Lib/test/test_ipaddress.py

@@ -986,6 +986,17 @@ def test_same_type_ordering(self):
             self.assertFalse(lhs >= rhs)
             self.assertFalse(rhs <= lhs)
 
+    def test_scoped_ipv6_ordering_same_ip(self):
+        # gh-151769: addresses with the same integer but different
+        # scope_id must be ordered; None < any string
+        unscoped = self.v6addr_scoped
+        scoped = ipaddress.IPv6Address(str(unscoped) + '%eth0')
+        self.assertNotEqual(unscoped, scoped)
+        self.assertLess(unscoped, scoped)
+        self.assertGreater(scoped, unscoped)
+        # sorted() must be deterministic
+        self.assertEqual(sorted([scoped, unscoped]), [unscoped, scoped])
+
     def test_containment(self):
         for obj in self.v4_addresses:
             self.assertIn(obj, self.v4net)

Misc/NEWS.d/next/Library/2026-06-22-00-00-00.gh-issue-151769.XxYyZz.rst

@@ -0,0 +1,3 @@
+Fix :class:`ipaddress.IPv6Address` ordering to account for ``scope_id``,
+so addresses with the same IP but different scope IDs compare as ordered
+and :func:`sorted` is deterministic.