Fix SF bug #472234: type(obj) calls type->tp_init (Roeland Rengelink)

The fix is a band-aid: type_call() now makes the same exception for a
single-argument call to type() as type_new() was already making.

Lib/test/test_descr.py

@@ -716,6 +716,18 @@ def metaclass():
             return "D" + self.__super._get_x()
     vereq(D().x, "DCBA")
 
+    # Make sure type(x) doesn't call x.__class__.__init__
+    class T(type):
+        counter = 0
+        def __init__(self, *args):
+            T.counter += 1
+    class C:
+        __metaclass__ = T
+    vereq(T.counter, 1)
+    a = C()
+    vereq(type(a), C)
+    vereq(T.counter, 1)
+
 def pymods():
     if verbose: print "Testing Python subclass of module..."
     log = []

Misc/ACKS

@@ -337,6 +337,7 @@ Sean Reifschneider
 Michael P. Reilly
 Bernhard Reiter
 Steven Reiz
+Roeland Rengelink
 Jan Pieter Riegel
 Armin Rigo
 Nicholas Riley

Objects/typeobject.c

@@ -147,6 +147,13 @@ type_call(PyTypeObject *type, PyObject *args, PyObject *kwds)
 
 	obj = type->tp_new(type, args, kwds);
 	if (obj != NULL) {
+		/* Ugly exception: when the call was type(something),
+		   don't call tp_init on the result. */
+		if (type == &PyType_Type &&
+		    PyTuple_Check(args) && PyTuple_GET_SIZE(args) == 1 &&
+		    (kwds == NULL ||
+		     (PyDict_Check(kwds) && PyDict_Size(kwds) == 0)))
+			return obj;
 		type = obj->ob_type;
 		if (type->tp_init != NULL &&
 		    type->tp_init(obj, args, kwds) < 0) {