Make test suite resilient to the absence of ctypes.

Lib/platform.py

@@ -678,7 +678,7 @@ def _platform(*args):
         if cleaned == platform:
             break
         platform = cleaned
-    while platform[-1] == '-':
+    while platform and platform[-1] == '-':
         platform = platform[:-1]
 
     return platform

Lib/test/test_platform.py

@@ -10,6 +10,14 @@
 from test import support
 from test.support import os_helper
 
+try:
+    # Some of the iOS tests need ctypes to operate.
+    # Confirm that the ctypes module is available
+    # is available.
+    import _ctypes
+except ImportError:
+    _ctypes = None
+
 FEDORA_OS_RELEASE = """\
 NAME=Fedora
 VERSION="32 (Thirty Two)"
@@ -229,8 +237,15 @@ def test_uname(self):
                 self.assertEqual(res.system, "Android")
                 self.assertEqual(res.release, platform.android_ver().release)
             elif sys.platform == "ios":
-                self.assertIn(res.system, {"iOS", "iPadOS"})
-                self.assertEqual(res.release, platform.ios_ver().release)
+                # Platform module needs ctypes for full operation. If ctypes
+                # isn't available, there's no ObjC module, and dummy values are
+                # returned.
+                if _ctypes:
+                    self.assertIn(res.system, {"iOS", "iPadOS"})
+                    self.assertEqual(res.release, platform.ios_ver().release)
+                else:
+                    self.assertEqual(res.system, "")
+                    self.assertEqual(res.release, "")
             else:
                 self.assertEqual(res.system, uname.sysname)
                 self.assertEqual(res.release, uname.release)
@@ -428,9 +443,10 @@ def test_mac_ver_with_fork(self):
 
     def test_ios_ver(self):
         result = platform.ios_ver()
-        if sys.platform == "ios":
-            system, release, model, is_simulator = result
 
+        # ios_ver is only fully available on iOS where ctypes is available.
+        if sys.platform == "ios" and _ctypes:
+            system, release, model, is_simulator = result
             # Result is a namedtuple
             self.assertEqual(result.system, system)
             self.assertEqual(result.release, release)

Lib/test/test_webbrowser.py

@@ -230,6 +230,7 @@ def _obj_ref(self, *args):
         # as a proxy for object instance references
         return "|".join(str(a) for a in args)
 
+    @unittest.skipIf(webbrowser.objc is None, "iOS Webbrowser tests require ctypes")
     def setUp(self):
         # Intercept the the objc library. Wrap the calls to get the
         # references to classes and selectors to return strings, and