[Zope] How to catalog all objects inherited from a certain class?

[Igor Elbert]

Hello,

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.

Any insight?

Thanks,
Igor