<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def get_assignable_book_ids(self, book_id):
 """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.* """

        # 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)