bpo-32107 - Improve MAC address calculation and fix test_uuid.py (#4600)

``uuid.getnode()`` now preferentially returns universally administered MAC addresses if available, over locally administered MAC addresses.  This makes a better guarantee for global uniqueness of UUIDs returned from ``uuid.uuid1()``.  If only locally administered MAC addresses are available, the first such one found is returned.

Also improve internal code style by being explicit about ``return None`` rather than falling off the end of the function.

Improve the test robustness.

1 files changed, 12 insertions, 14 deletions

diff --git a/Lib/test/test_uuid.py b/Lib/test/test_uuid.py
index 083c2aa8aab..f113c551209 100644
--- a/Lib/test/test_uuid.py
+++ b/Lib/test/test_uuid.py
@@ -512,59 +512,57 @@ eth0      Link encap:Ethernet  HWaddr 12:34:56:78:90:ab
 
         self.assertEqual(mac, 0x1234567890ab)
 
-    def check_node(self, node, requires=None, network=False):
+    def check_node(self, node, requires=None):
         if requires and node is None:
             self.skipTest('requires ' + requires)
         hex = '%012x' % node
         if support.verbose >= 2:
             print(hex, end=' ')
-        if network:
-            # 47 bit will never be set in IEEE 802 addresses obtained
-            # from network cards.
-            self.assertFalse(node & 0x010000000000, hex)
         self.assertTrue(0 < node < (1 << 48),
                         "%s is not an RFC 4122 node ID" % hex)
 
     @unittest.skipUnless(os.name == 'posix', 'requires Posix')
     def test_ifconfig_getnode(self):
         node = self.uuid._ifconfig_getnode()
-        self.check_node(node, 'ifconfig', True)
+        self.check_node(node, 'ifconfig')
 
     @unittest.skipUnless(os.name == 'posix', 'requires Posix')
     def test_ip_getnode(self):
         node = self.uuid._ip_getnode()
-        self.check_node(node, 'ip', True)
+        self.check_node(node, 'ip')
 
     @unittest.skipUnless(os.name == 'posix', 'requires Posix')
     def test_arp_getnode(self):
         node = self.uuid._arp_getnode()
-        self.check_node(node, 'arp', True)
+        self.check_node(node, 'arp')
 
     @unittest.skipUnless(os.name == 'posix', 'requires Posix')
     def test_lanscan_getnode(self):
         node = self.uuid._lanscan_getnode()
-        self.check_node(node, 'lanscan', True)
+        self.check_node(node, 'lanscan')
 
     @unittest.skipUnless(os.name == 'posix', 'requires Posix')
     def test_netstat_getnode(self):
         node = self.uuid._netstat_getnode()
-        self.check_node(node, 'netstat', True)
+        self.check_node(node, 'netstat')
 
     @unittest.skipUnless(os.name == 'nt', 'requires Windows')
     def test_ipconfig_getnode(self):
         node = self.uuid._ipconfig_getnode()
-        self.check_node(node, 'ipconfig', True)
+        self.check_node(node, 'ipconfig')
 
     @unittest.skipUnless(importable('win32wnet'), 'requires win32wnet')
     @unittest.skipUnless(importable('netbios'), 'requires netbios')
     def test_netbios_getnode(self):
         node = self.uuid._netbios_getnode()
-        self.check_node(node, network=True)
+        self.check_node(node)
 
     def test_random_getnode(self):
         node = self.uuid._random_getnode()
-        # Least significant bit of first octet must be set.
-        self.assertTrue(node & 0x010000000000, '%012x' % node)
+        # The multicast bit, i.e. the least significant bit of first octet,
+        # must be set for randomly generated MAC addresses.  See RFC 4122,
+        # $4.1.6.
+        self.assertTrue(node & (1 << 40), '%012x' % node)
         self.check_node(node)
 
     @unittest.skipUnless(os.name == 'posix', 'requires Posix')