py3: Make metaclass work on both python2 and python3.

product/ERP5Type/Utils.py

@@ -566,6 +566,41 @@ else:
   def unicode2str(s):
     return s
 
+def with_metaclass(meta, *bases):
+  """
+  Function from jinja2/_compat.py. License: BSD (copy/paste here for
+  ExtensionClass)
+
+  Use it like this::
+      class BaseForm(object):
+          pass
+
+      class FormType(type):
+          pass
+
+      class Form(with_metaclass(FormType, BaseForm)):
+          pass
+
+  This requires a bit of explanation: the basic idea is to make a
+  dummy metaclass for one level of class instantiation that replaces
+  itself with the actual metaclass.  Because of internal type checks
+  we also need to make sure that we downgrade the custom metaclass
+  for one level to something closer to type (that's why __call__ and
+  __init__ comes back from type etc.).
+
+  This has the advantage over six.with_metaclass of not introducing
+  dummy classes into the final MRO.
+  """
+  class metaclass(meta):
+    __call__ = type.__call__
+    __init__ = type.__init__
+    def __new__(cls, name, this_bases, d):
+      if this_bases is None:
+        import ExtensionClass
+        return ExtensionClass.ExtensionClass.__new__(cls, name, (), d)
+      return meta(name, bases, d)
+  return metaclass('temporary_class', None, {})
+
 #####################################################
 # Globals initialization
 #####################################################

product/ERP5Type/mixin/component.py

@@ -122,7 +122,8 @@ class RecordablePropertyMetaClass(ExtensionClass):
     # ghosting/unghosting Portal Types
     return ExtensionClass.__new__(ExtensionClass, name, bases, dictionary)
 
-class ComponentMixin(PropertyRecordableMixin, Base):
+from Products.ERP5Type.Utils import with_metaclass
+class ComponentMixin(with_metaclass(RecordablePropertyMetaClass, type('NewBase', (PropertyRecordableMixin, Base), {}))):
   """
   Mixin used for all ZODB Components. Most of the code is generic, thus actual
   ZODB Components should have almost nothing to defined...
@@ -145,8 +146,6 @@ class ComponentMixin(PropertyRecordableMixin, Base):
   state, checkConsistency() is called to check id, reference, version and
   errors/warnings messages (set when the Component is modified).
   """
-  __metaclass__ = RecordablePropertyMetaClass
-
   isPortalContent = 1
   isRADContent = 1
   isDelivery = ConstantGetter('isDelivery', value=True)