Merged revisions 55545-55587 via svnmerge from

svn+ssh://pythondev@svn.python.org/python/branches/p3yk

........
  r55587 | guido.van.rossum | 2007-05-25 10:37:01 -0700 (Fri, 25 May 2007) | 2 lines

  Implement isinstance and issubclass overriding, a la PEP 3119.
........

Lib/test/test_typechecks.py

+"""Unit tests for __instancecheck__ and __subclasscheck__."""
+
+import unittest
+from test import test_support
+
+
+class ABC(type):
+
+    def __instancecheck__(cls, inst):
+        """Implement isinstance(inst, cls)."""
+        return any(cls.__subclasscheck__(c)
+                   for c in {type(inst), inst.__class__})
+
+    def __subclasscheck__(cls, sub):
+        """Implement issubclass(sub, cls)."""
+        candidates = cls.__dict__.get("__subclass__", set()) | {cls}
+        return any(c in candidates for c in sub.mro())
+
+
+class Integer(metaclass=ABC):
+
+    __subclass__ = {int}
+
+
+class SubInt(Integer):
+
+    pass
+
+
+class Evil:
+    def __instancecheck__(self, inst): return False
+
+
+class TypeChecksTest(unittest.TestCase):
+
+    def testIsSubclassInternal(self):
+        self.assertEqual(Integer.__subclasscheck__(int), True)
+        self.assertEqual(Integer.__subclasscheck__(float), False)
+
+    def testIsSubclassBuiltin(self):
+        self.assertEqual(issubclass(int, Integer), True)
+        self.assertEqual(issubclass(float, Integer), False)
+
+    def testIsInstanceBuiltin(self):
+        self.assertEqual(isinstance(42, Integer), True)
+        self.assertEqual(isinstance(3.14, Integer), False)
+
+    def testIsInstanceActual(self):
+        self.assertEqual(isinstance(Integer(), Integer), True)
+
+    def testIsSubclassActual(self):
+        self.assertEqual(issubclass(Integer, Integer), True)
+
+    def testSubclassBehavior(self):
+        self.assertEqual(issubclass(SubInt, Integer), True)
+        self.assertEqual(issubclass(SubInt, SubInt), True)
+        self.assertEqual(issubclass(Integer, SubInt), False)
+        self.assertEqual(issubclass(int, SubInt), False)
+        self.assertEqual(isinstance(SubInt(), Integer), True)
+        self.assertEqual(isinstance(SubInt(), SubInt), True)
+        self.assertEqual(isinstance(42, SubInt), False)
+
+    def testInfiniteRecursionCaughtProperly(self):
+        e = Evil()
+        # This invokes isinstance() recursively, until the stack is exhausted.
+        self.assertRaises(RuntimeError, isinstance, e, Evil)
+        # XXX How to check the same situation for issubclass()?
+
+
+def test_main():
+    test_support.run_unittest(TypeChecksTest)
+
+
+if __name__ == "__main__":
+    unittest.main()

Objects/abstract.c

@@ -2130,6 +2130,24 @@ recursive_isinstance(PyObject *inst, PyObject *cls, int recursion_depth)
 int
 PyObject_IsInstance(PyObject *inst, PyObject *cls)
 {
+	PyObject *t, *v, *tb;
+	PyErr_Fetch(&t, &v, &tb);
+	PyObject *checker = PyObject_GetAttrString(cls, "__instancecheck__");
+	PyErr_Restore(t, v, tb);
+	if (checker != NULL) {
+		PyObject *res;
+		int ok = -1;
+		if (Py_EnterRecursiveCall(" in __instancecheck__"))
+			return ok;
+		res = PyObject_CallFunctionObjArgs(checker, inst, NULL);
+		Py_LeaveRecursiveCall();
+		Py_DECREF(checker);
+		if (res != NULL) {
+			ok = PyObject_IsTrue(res);
+			Py_DECREF(res);
+		}
+		return ok;
+	}
 	return recursive_isinstance(inst, cls, Py_GetRecursionLimit());
 }
 
@@ -2180,6 +2198,24 @@ recursive_issubclass(PyObject *derived, PyObject *cls, int recursion_depth)
 int
 PyObject_IsSubclass(PyObject *derived, PyObject *cls)
 {
+	PyObject *t, *v, *tb;
+	PyErr_Fetch(&t, &v, &tb);
+	PyObject *checker = PyObject_GetAttrString(cls, "__subclasscheck__");
+	PyErr_Restore(t, v, tb);
+	if (checker != NULL) {
+		PyObject *res;
+		int ok = -1;
+		if (Py_EnterRecursiveCall(" in __subclasscheck__"))
+			return ok;
+		res = PyObject_CallFunctionObjArgs(checker, derived, NULL);
+		Py_LeaveRecursiveCall();
+		Py_DECREF(checker);
+		if (res != NULL) {
+			ok = PyObject_IsTrue(res);
+			Py_DECREF(res);
+		}
+		return ok;
+	}
 	return recursive_issubclass(derived, cls, Py_GetRecursionLimit());
 }