code: def find_class(self, cls):
          
          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__))
docs: Given a Python `cls` object, try to find it in this module
          or in any of the exported identifiers of the submodules.