bpo-40570: Improve compatibility of uname_result with late-bound .platform (#20015)

* bpo-40570: Improve compatibility of uname_result with late-bound .platform.

* Add test capturing ability to cast uname to a tuple.

Author: jaraco

Lib/platform.py

@@ -798,9 +798,10 @@ def __iter__(self):
         )
 
     def __getitem__(self, key):
-        if key == 5:
-            return self.processor
-        return super().__getitem__(key)
+        return tuple(iter(self))[key]
+
+    def __len__(self):
+        return len(tuple(iter(self)))
 
 
 _uname_cache = None

Lib/test/test_platform.py

@@ -154,11 +154,26 @@ def test_uname(self):
         res = platform.uname()
         self.assertTrue(any(res))
         self.assertEqual(res[0], res.system)
+        self.assertEqual(res[-6], res.system)
         self.assertEqual(res[1], res.node)
+        self.assertEqual(res[-5], res.node)
         self.assertEqual(res[2], res.release)
+        self.assertEqual(res[-4], res.release)
         self.assertEqual(res[3], res.version)
+        self.assertEqual(res[-3], res.version)
         self.assertEqual(res[4], res.machine)
+        self.assertEqual(res[-2], res.machine)
         self.assertEqual(res[5], res.processor)
+        self.assertEqual(res[-1], res.processor)
+        self.assertEqual(len(res), 6)
+
+    def test_uname_cast_to_tuple(self):
+        res = platform.uname()
+        expected = (
+            res.system, res.node, res.release, res.version, res.machine,
+            res.processor,
+        )
+        self.assertEqual(tuple(res), expected)
 
     @unittest.skipIf(sys.platform in ['win32', 'OpenVMS'], "uname -p not used")
     def test_uname_processor(self):