Igor Elbert writes:

I am looking for a way to catalog all objects inherited from my class. Objects may have different meta_types so I can't use obj_metatypes=['MyClass'].

I found that ZCatalog uses ZopeFind for the search. ZopeFind has a parameter obj_expr that gets evaluated on the fly. I would like to say something like ZopeFind(..., obj_expr='isinstance(self, MyClass)' ) but I don't know how. "isinstance" is not available in TTW code (it would not work).

One trick, often used in Zope is to provide indicating attributes, e.g. "isPrincipiaFolderish" indicates a Zope Folder (and its derivatives). You must be careful, that the attribute is not acquired. Safely, this is only possible in an External Method. You can appriximate it in TTW code with obj_expr="_.hasattr(aq_explicit,'mySpecialAttribute')" The alternative is to use an External Method "checkMyClass" in obj_expr="checkMyClass(this())" with def checkMyClass(self): from Acquisition import aq_base return isinstance(aq_base(self),MyClass) Dieter