Fix a regression in uuid added in bpo-32107. (#4677)

uuid.get_node() always must return a stable result.
Also added a test for non-reproducibility of _random_getnode().
Original patch by Xavier de Gaye.

Lib/test/test_uuid.py

@@ -565,6 +565,9 @@ eth0      Link encap:Ethernet  HWaddr 12:34:56:78:90:ab
         self.assertTrue(node & (1 << 40), '%012x' % node)
         self.check_node(node)
 
+        node2 = self.uuid._random_getnode()
+        self.assertNotEqual(node2, node, '%012x' % node)
+
     @unittest.skipUnless(os.name == 'posix', 'requires Posix')
     def test_unix_getnode(self):
         if not importable('_uuid') and not importable('ctypes'):

Lib/uuid.py

@@ -674,14 +674,14 @@ def getnode():
         getters = [_unix_getnode, _ifconfig_getnode, _ip_getnode,
                    _arp_getnode, _lanscan_getnode, _netstat_getnode]
 
-    for getter in getters:
+    for getter in getters + [_random_getnode]:
         try:
             _node = getter()
         except:
             continue
         if _node is not None:
             return _node
-    return _random_getnode()
+    assert False, '_random_getnode() returned None'
 
 
 _last_timestamp = None