Hi all,
I recently posted to the cython-users list about this problem. This
email is to submita potential patch to fix the issue. The issue is as
follows:
At Enthought we are busy porting Traits
(http://github.com/enthought/traits) from C to Cython.
An issue has come up that that prevents classes inheriting from a
cdef-class from playing nicely with ABCs. It is type's tp_new that
checks for abstractmethods that have not been implemented, so if type's
tp_new is bypassed, the check is never run and you can instantiate an
abstract base class.
It is equivalent to this simple example below (taken from
http://stackoverflow.com/questions/20432335). If you replace the simple
class A with a Cython cdef class, the effect is the same.
import abc
class A(object):
def __new__(cls):
# self = object.__new__(cls)
return 42
class B(A):
__metaclass__ = abc.ABCMeta
@abc.abstractmethod
def foo(self):
pass
b = B() # No exception.
Thanks,
Simon
From 80d518908ad3f2052e4d9e7fcf8101fc5d75280e Mon Sep 17 00:00:00 2001
From: Simon Jagoe <si...@simonjagoe.com>
Date: Wed, 8 Jan 2014 20:00:48 +0000
Subject: [PATCH] BUG: Call PyBaseObject_Type.tp_new instead of
NewType->tp_alloc
---
Cython/Compiler/ModuleNode.py | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/Cython/Compiler/ModuleNode.py b/Cython/Compiler/ModuleNode.py
index 338efc0..c2795fe 100644
--- a/Cython/Compiler/ModuleNode.py
+++ b/Cython/Compiler/ModuleNode.py
@@ -1134,7 +1134,7 @@ class ModuleNode(Nodes.Node, Nodes.BlockNode):
if scope.needs_gc():
code.putln("PyObject_GC_Track(o);")
code.putln("} else {")
- code.putln("o = (*t->tp_alloc)(t, 0);")
+ code.putln("o = (PyObject *) PyBaseObject_Type.tp_new(t, __pyx_empty_tuple, 0);")
code.putln("if (unlikely(!o)) return 0;")
if freelist_size and not base_type:
code.putln('}')
--
1.8.3.2
_______________________________________________
cython-devel mailing list
cython-devel@python.org
https://mail.python.org/mailman/listinfo/cython-devel
