Patch #1601678: move intern() to sys.intern().

Lib/test/test_sys.py

@@ -350,6 +350,31 @@ class SysModuleTest(unittest.TestCase):
         # the test runs under regrtest.
         self.assert_(sys.__stdout__.encoding == sys.__stderr__.encoding)
 
+    def test_intern(self):
+        self.assertRaises(TypeError, sys.intern)
+        s = "never interned before"
+        self.assert_(sys.intern(s) is s)
+        s2 = s.swapcase().swapcase()
+        self.assert_(sys.intern(s2) is s)
+
+        # Subclasses of string can't be interned, because they
+        # provide too much opportunity for insane things to happen.
+        # We don't want them in the interned dict and if they aren't
+        # actually interned, we don't want to create the appearance
+        # that they are by allowing intern() to succeeed.
+        class S(str):
+            def __hash__(self):
+                return 123
+
+        self.assertRaises(TypeError, sys.intern, S("abc"))
+
+        # It's still safe to pass these strings to routines that
+        # call intern internally, e.g. PyObject_SetAttr().
+        s = S("abc")
+        setattr(s, s, s)
+        self.assertEqual(getattr(s, s), s)
+
+
 def test_main():
     test.test_support.run_unittest(SysModuleTest)