code: def get_assignable_book_ids(self, book_id):
          
          # Implemented from template for
          # osid.resource.ResourceBinAssignmentSession.get_assignable_bin_ids
          # This will likely be overridden by an authorization adapter
          mgr = self._get_provider_manager('COMMENTING', local=True)
          lookup_session = mgr.get_book_lookup_session(proxy=self._proxy)
          books = lookup_session.get_books()
          id_list = []
          for book in books:
              id_list.append(book.get_id())
          return IdList(id_list)
docs: Gets a list of books including and under the given book node in which any comment can be assigned.
  
          arg:    book_id (osid.id.Id): the ``Id`` of the ``Book``
          return: (osid.id.IdList) - list of assignable book ``Ids``
          raise:  NullArgument - ``book_id`` is ``null``
          raise:  OperationFailed - unable to complete request
          *compliance: mandatory -- This method must be implemented.*