docs: def get_comments_by_books(self, book_ids):
          """Gets the list of ``Comments`` corresponding to a list of ``Books``.
  
          arg:    book_ids (osid.id.IdList): list of book ``Ids``
          return: (osid.commenting.CommentList) - list of comments
          raise:  NullArgument - ``book_ids`` is ``null``
          raise:  OperationFailed - unable to complete request
          raise:  PermissionDenied - authorization failure
          *compliance: mandatory -- This method must be implemented.*
  
          """
          # Implemented from template for
          # osid.resource.ResourceBinSession.get_resources_by_bins
          comment_list = []
          for book_id in book_ids:
              comment_list += list(
                  self.get_comments_by_book(book_id))
          return objects.CommentList(comment_list)