gh-129538: Fix IPv6Interface.ip losing scope ID information

Lib/ipaddress.py

@@ -2239,7 +2239,8 @@ def __hash__(self):
 
     @property
     def ip(self):
-        return IPv6Address(self._ip)
+        addr_str = self._string_from_ip_int(self._ip) + (f'%{self._scope_id}' if self._scope_id else '')
+        return IPv6Address(addr_str)
 
     @property
     def with_prefixlen(self):

Lib/test/test_ipaddress.py

@@ -562,6 +562,11 @@ def test_copy(self):
         self.assertEqual(addr, copy.copy(addr))
         self.assertEqual(addr, copy.deepcopy(addr))
 
+    def test_ipv6_interface_scope_id(self):
+        addr = ipaddress.IPv6Address("fe80::%10")
+        addr_with_prefix = ipaddress.IPv6Interface((addr, 64))
+        self.assertEqual(addr_with_prefix.ip, ipaddress.IPv6Address("fe80::%10"))
+
 
 class NetmaskTestMixin_v4(CommonTestMixin_v4):
     """Input validation on interfaces and networks is very similar"""

Misc/NEWS.d/next/Library/2025-02-01-13-01-12.gh-issue-129538.A9ERy9.rst

@@ -0,0 +1,21 @@
+This pull request addresses the issue described in `issue #129538 <https://github.com/python/cpython/issues/129538>`_, where the ``IPv6Interface.ip`` loses the scope ID information when accessing the IP address.
+
+The problem occurs when an IPv6 address with a scope ID is converted into an ``IPv6Interface`` and then accessed via the ``ip`` property, resulting in the loss of the scope ID information. This behavior is unexpected and not documented.
+
+Minimal Example Demonstrating the Issue::
+
+   addr = ipaddress.IPv6Address("fe80::%10")
+   addr_with_prefix = ipaddress.IPv6Interface((addr, 64))
+   print(addr_with_prefix.ip)  # Expected: IPv6Address('fe80::%10'), Actual: IPv6Address('fe80::')
+
+Changes Made:
+1. Fix in ``IPv6Interface`` Class:
+   - Updated the ``IPv6Interface`` class to ensure the scope ID is preserved when converting the IP address.
+   - Modified the ``ip`` property to include the scope ID in the address string.
+
+2. Added Test Case:
+   - Added a test case to verify that the scope ID is preserved when converting the IP address in the ``IPv6Interface`` class.
+
+Tests and Documentation:
+- Updated the tests in ``Lib/test/test_ipaddress.py`` to include the new test case.
+- No changes to documentation as the behavior is expected and intuitive.