[Zope-dev] new BTreeContainer implementation, please review

[Christophe Combelles]

Hi,

While fixing some bugs in zope.app.container,
I've also modified the implementation of the BTreeContainer,
by not inheriting from the SampleContainer, and directly accessing the btree. 
This had remained as a TODO in the btree.py file, so I did it, but...

The result is all previous persisted BTreeContainers (such as PrincipalFolder) 
are broken because the btree used to be stored in self._SampleContainer__data, 
while the new implementation stores it in self._BTreeContainer__data.

So I've added a property to offer a transparent backward compatibility:

     def _get__data(self):
         try:
             return self._BTreeContainer__data
         except:
             return self._SampleContainer__data
     def _set__data(self, value):
         try:
             self._BTreeContainer__data = value
         except:
             self._SampleContainer__data = value
     def _del_data(self):
         try:
             del self._BTreeContainer__data
         except:
             del self._SampleContainer__data
     __data = property(_get__data, _set__data, _del_data)



Do you think it is safe? Is there any better solution for this? Should I rather 
write an evolution script? Or should I revert all this back to inheriting from 
SampleContainer?

Christophe