SF bug #753451: classmethod abuse --> SystemError

Check the argument to classmethod for callability.

Backport candidate.

Lib/test/test_descr.py

@@ -1485,6 +1485,14 @@ def classmethods():
     vereq(super(D,D).goo(), (D,))
     vereq(super(D,d).goo(), (D,))
 
+    # Verify that argument is checked for callability (SF bug 753451)
+    try:
+        classmethod(1).__get__(1)
+    except TypeError:
+        pass
+    else:
+        raise TestFailed, "classmethod should check for callability"
+
 def classmethods_in_c():
     if verbose: print "Testing C-based class methods..."
     import xxsubtype as spam

Objects/funcobject.c

@@ -640,6 +640,12 @@ cm_init(PyObject *self, PyObject *args, PyObject *kwds)
 
 	if (!PyArg_UnpackTuple(args, "classmethod", 1, 1, &callable))
 		return -1;
+	if (!PyCallable_Check(callable)) {
+		PyErr_Format(PyExc_TypeError, "'%s' object is not callable",
+		     callable->ob_type->tp_name);
+		return -1;
+	}
+	
 	Py_INCREF(callable);
 	cm->cm_callable = callable;
 	return 0;