Broken object migration with ZODB

migrate.py

import imp
import sys

def create_modules(module_path):
    path = ""
    module = None
    for element in module_path.split('.'):
        path += element

        try:
            module = __import__(path)
        except ImportError:
            new = imp.new_module(path)
            if module is not None:
                setattr(module, element, new)
            module = new

        sys.modules[path] = module
        __import__(path)

        path += "."

    return module

def stub(module_path, class_name, base_class, meta_class=type):
    module = create_modules(module_path)
    cls = meta_class(class_name, (base_class, ), {})
    setattr(module, class_name, cls)

def migrate(self):
    # import known base class (or best match!)
    from Products.ATContentTypes.content.folder import ATFolder

    # stub out broken class
    stub('Products.MyOldBrokenProduct.SomeClass', 'SomeClass', ATFolder)

    # enjoy
    print self['some_old_site'].portal_old_broken_tool.valuable_data

You can now stub out Zope interfaces using:

stub('some.package.interfaces', 'IMyInterface', zope.interface.Interface, zope.interface.interface.InterfaceClass)

NB: This only works for classes that are pickled into a dict, which, thankfully, means most of them.