SF bug [#470040] ParseTuple t# vs subclasses.

inherit_slots():  tp_as_buffer was getting inherited as if it were a
method pointer, rather than a pointer to a vector of method pointers.  As
a result, inheriting from a type that implemented buffer methods was
ineffective, leaving all the tp_as_buffer slots NULL in the subclass.

Lib/test/test_descr.py

@@ -2299,6 +2299,36 @@ def subclasspropagation():
     else:
         raise TestFailed, "d.foo should be undefined now"
 
+def buffer_inherit():
+    import binascii
+    # SF bug [#470040] ParseTuple t# vs subclasses.
+    if verbose:
+        print "Testing that buffer interface is inherited ..."
+
+    class MyStr(str):
+        pass
+    base = 'abc'
+    m = MyStr(base)
+    # b2a_hex uses the buffer interface to get its argument's value, via
+    # PyArg_ParseTuple 't#' code.
+    vereq(binascii.b2a_hex(m), binascii.b2a_hex(base))
+
+    # It's not clear that unicode will continue to support the character
+    # buffer interface, and this test will fail if that's taken away.
+    class MyUni(unicode):
+        pass
+    base = u'abc'
+    m = MyUni(base)
+    vereq(binascii.b2a_hex(m), binascii.b2a_hex(base))
+
+    class MyInt(int):
+        pass
+    m = MyInt(42)
+    try:
+        binascii.b2a_hex(m)
+        raise TestFailed('subclass of int should not have a buffer interface')
+    except TypeError:
+        pass
 
 def test_main():
     class_docstrings()
@@ -2347,6 +2377,7 @@ def test_main():
     copies()
     binopoverride()
     subclasspropagation()
+    buffer_inherit()
     if verbose: print "All OK"
 
 if __name__ == "__main__":

Objects/typeobject.c

@@ -1657,6 +1657,7 @@ inherit_slots(PyTypeObject *type, PyTypeObject *base)
 #define COPYNUM(SLOT) COPYSLOT(tp_as_number->SLOT)
 #define COPYSEQ(SLOT) COPYSLOT(tp_as_sequence->SLOT)
 #define COPYMAP(SLOT) COPYSLOT(tp_as_mapping->SLOT)
+#define COPYBUF(SLOT) COPYSLOT(tp_as_buffer->SLOT)
 
 	/* This won't inherit indirect slots (from tp_as_number etc.)
 	   if type doesn't provide the space. */
@@ -1732,6 +1733,16 @@ inherit_slots(PyTypeObject *type, PyTypeObject *base)
 		COPYMAP(mp_ass_subscript);
 	}
 
+	if (type->tp_as_buffer != NULL && base->tp_as_buffer != NULL) {
+		basebase = base->tp_base;
+		if (basebase->tp_as_buffer == NULL)
+			basebase = NULL;
+		COPYBUF(bf_getreadbuffer);
+		COPYBUF(bf_getwritebuffer);
+		COPYBUF(bf_getsegcount);
+		COPYBUF(bf_getcharbuffer);
+	}
+
 	basebase = base->tp_base;
 
 	COPYSLOT(tp_dealloc);
@@ -1749,7 +1760,6 @@ inherit_slots(PyTypeObject *type, PyTypeObject *base)
 	/* tp_hash see tp_richcompare */
 	COPYSLOT(tp_call);
 	COPYSLOT(tp_str);
-	COPYSLOT(tp_as_buffer);
 	if (type->tp_flags & base->tp_flags & Py_TPFLAGS_HAVE_RICHCOMPARE) {
 		if (type->tp_compare == NULL &&
 		    type->tp_richcompare == NULL &&