Given a Python `cls` object, try to find it in this module
        or in any of the exported identifiers of the submodules.

def find_class(self, cls):
        """
        Given a Python `cls` object, try to find it in this module
        or in any of the exported identifiers of the submodules.
        """
        for doc_cls in self.classes():
            if cls is doc_cls.cls:
                return doc_cls
        for module in self.submodules():
            doc_cls = module.find_class(cls)
            if not isinstance(doc_cls, External):
                return doc_cls
        return External('%s.%s' % (cls.__module__, cls.__name__))