bpo-35516: Add macOS support to platform.system_alias()

Doc/library/platform.rst

@@ -155,6 +155,11 @@ Cross Platform
    for some systems.  It also does some reordering of the information in some cases
    where it would otherwise cause confusion.
 
+   .. versionchanged:: 3.8
+      On macOS, the function now uses :func:`mac_ver`, if it returns a
+      non-empty release string, to get the macOS version rather than the darwin
+      version.
+
 
 .. function:: version()
 

Lib/platform.py

@@ -478,7 +478,14 @@ def system_alias(system, release, version):
         where it would otherwise cause confusion.
 
     """
-    if system == 'SunOS':
+    if system == 'Darwin':
+        # macOS (darwin kernel)
+        macos_release = mac_ver()[0]
+        if macos_release:
+            system = 'macOS'
+            release = macos_release
+
+    elif system == 'SunOS':
         # Sun's OS
         if release < '5':
             # These releases use the old name SunOS

Lib/test/test_platform.py

@@ -352,30 +352,41 @@ def test__comparable_version(self):
     def test_macos(self):
         self.addCleanup(self.clear_caches)
 
+        darwin_version = ('Darwin Kernel Version 17.7.0: '
+                          'Thu Jun 21 22:53:14 PDT 2018; '
+                          'root:xnu-4570.71.2~1/RELEASE_X86_64')
         uname = ('Darwin', 'hostname', '17.7.0',
-                 ('Darwin Kernel Version 17.7.0: '
-                  'Thu Jun 21 22:53:14 PDT 2018; '
-                  'root:xnu-4570.71.2~1/RELEASE_X86_64'),
+                 darwin_version,
                  'x86_64', 'i386')
+        uname = platform.uname_result(*uname)
         arch = ('64bit', '')
         with mock.patch.object(platform, 'uname', return_value=uname), \
              mock.patch.object(platform, 'architecture', return_value=arch):
-            for mac_ver, expected_terse, expected in [
+            for mac_ver, expected_terse, expected, expected_system_alias in [
                 # darwin: mac_ver() returns empty strings
                 (('', '', ''),
                  'Darwin-17.7.0',
-                 'Darwin-17.7.0-x86_64-i386-64bit'),
+                 'Darwin-17.7.0-x86_64-i386-64bit',
+                 ('Darwin', '17.7.0', darwin_version)),
                 # macOS: mac_ver() returns macOS version
                 (('10.13.6', ('', '', ''), 'x86_64'),
                  'macOS-10.13.6',
-                 'macOS-10.13.6-x86_64-i386-64bit'),
+                 'macOS-10.13.6-x86_64-i386-64bit',
+                 ('macOS', '10.13.6', darwin_version)),
             ]:
                 with mock.patch.object(platform, 'mac_ver',
                                        return_value=mac_ver):
                     self.clear_caches()
                     self.assertEqual(platform.platform(terse=1), expected_terse)
                     self.assertEqual(platform.platform(), expected)
 
+                    plat_uname = platform.uname()
+                    system_alias = platform.system_alias(plat_uname.system,
+                                                         plat_uname.release,
+                                                         plat_uname.version)
+                    self.assertEqual(system_alias,
+                                     expected_system_alias)
+
 
 if __name__ == '__main__':
     unittest.main()

Misc/NEWS.d/next/Library/2018-12-17-10-34-05.bpo-35516.0g2Vn4.rst

@@ -0,0 +1,2 @@
+On macOS, :func:`platform.system_alias` now returns macOS and macOS release,
+rather than Darwin and Darwin release.