See:

https://mail.gnome.org/archives/xml/2013-April/msg00039.html

--- libxml2-2.9.1/python/libxml_wrap.h	2013-04-01 19:25:28.000000000 -0700
+++ libxml2-2.9.1/python/libxml_wrap.h	2013-04-23 07:55:11.268714627 -0700
@@ -34,11 +34,11 @@
 #define PyBytes_AsString PyString_AsString
 #define PyBytes_AS_STRING PyString_AS_STRING
 #define PyBytes_GET_SIZE PyString_GET_SIZE
-
+#endif
+#ifndef PyCapsule_New
 #define PyCapsule_New PyCObject_FromVoidPtrAndDesc
 #define PyCapsule_CheckExact PyCObject_Check
 #define PyCapsule_GetPointer(o, n) PyCObject_GetDesc((o))
-
 #endif
 #endif