gh-109466: Add ipv6_mapped property to IPv4Address (#109467)

Adds the `IPv4Address.ipv6_mapped` property.

Co-authored-by: Hugo van Kemenade <hugovk@users.noreply.github.com>

2 files changed, 18 insertions, 0 deletions

diff --git a/Lib/ipaddress.py b/Lib/ipaddress.py
index 68ddfbe..e398cc1 100644
--- a/Lib/ipaddress.py
+++ b/Lib/ipaddress.py
@@ -1389,6 +1389,16 @@ class IPv4Address(_BaseV4, _BaseAddress):
         """
         return self in self._constants._linklocal_network
 
+    @property
+    def ipv6_mapped(self):
+        """Return the IPv4-mapped IPv6 address.
+
+        Returns:
+            The IPv4-mapped IPv6 address per RFC 4291.
+
+        """
+        return IPv6Address(f'::ffff:{self}')
+
 
 class IPv4Interface(IPv4Address):
 
diff --git a/Lib/test/test_ipaddress.py b/Lib/test/test_ipaddress.py
index 33a0f98..b4952ac 100644
--- a/Lib/test/test_ipaddress.py
+++ b/Lib/test/test_ipaddress.py
@@ -303,6 +303,14 @@ class AddressTestCase_v4(BaseTestCase, CommonTestMixin_v4):
     def test_weakref(self):
         weakref.ref(self.factory('192.0.2.1'))
 
+    def test_ipv6_mapped(self):
+        self.assertEqual(ipaddress.IPv4Address('192.168.1.1').ipv6_mapped,
+                         ipaddress.IPv6Address('::ffff:192.168.1.1'))
+        self.assertEqual(ipaddress.IPv4Address('192.168.1.1').ipv6_mapped,
+                         ipaddress.IPv6Address('::ffff:c0a8:101'))
+        self.assertEqual(ipaddress.IPv4Address('192.168.1.1').ipv6_mapped.ipv4_mapped,
+                         ipaddress.IPv4Address('192.168.1.1'))
+
 
 class AddressTestCase_v6(BaseTestCase, CommonTestMixin_v6):
     factory = ipaddress.IPv6Address