gh-153769: Clarify the TypeError from ipaddress subnet_of()/supernet_of()

Lib/ipaddress.py

@@ -1033,8 +1033,9 @@ def _is_subnet_of(a, b):
             return (b.network_address <= a.network_address and
                     b.broadcast_address >= a.broadcast_address)
         except AttributeError:
-            raise TypeError(f"Unable to test subnet containment "
-                            f"between {a} and {b}")
+            raise TypeError(
+                f"Unable to test subnet containment between {a} and {b}: "
+                f"both must be network objects") from None
 
     def subnet_of(self, other):
         """Return True if this network is a subnet of other."""

Lib/test/test_ipaddress.py

@@ -723,6 +723,19 @@ def test_subnet_of_mixed_types(self):
             ipaddress.IPv6Network('::1/128').subnet_of(
                 ipaddress.IPv4Network('10.0.0.0/30'))
 
+    def test_subnet_of_non_network(self):
+        # Passing something that is not a network object (e.g. an address)
+        # must raise a clear TypeError rather than masking an internal
+        # AttributeError (gh-153769).
+        net = ipaddress.IPv4Network('10.0.0.0/30')
+        for other in (ipaddress.IPv4Address('10.0.0.1'), '10.0.0.0/30', 42):
+            for method in (net.subnet_of, net.supernet_of):
+                with self.assertRaises(TypeError) as cm:
+                    method(other)
+                self.assertIn('network', str(cm.exception))
+                # The internal AttributeError is not shown to the caller.
+                self.assertTrue(cm.exception.__suppress_context__)
+
 
 class NetmaskTestMixin_v6(CommonTestMixin_v6):
     """Input validation on interfaces and networks is very similar"""

Misc/ACKS

@@ -2008,6 +2008,7 @@ Wm. Keith van der Meulen
 Eric N. Vander Weele
 Andrew Vant
 Atul Varma
+Vyron Vasileiadis
 Dmitry Vasiliev
 Sebastian Ortiz Vasquez
 Alexandre Vassalotti

Misc/NEWS.d/next/Library/2026-07-19-16-30-00.gh-issue-153769.STygbq.rst

@@ -0,0 +1,4 @@
+:meth:`~ipaddress.IPv4Network.subnet_of` and
+:meth:`~ipaddress.IPv4Network.supernet_of` now say that both arguments must be
+network objects when passed something else, such as an address, and no longer
+show the internal :exc:`AttributeError` behind it.