def update_fpointer(self, nid, mode=ADD):
        """set _fpointer recursively"""
        if nid is None:
            return

        if mode is self.ADD:
            self._fpointer.append(nid)
        elif mode is self.DELETE:
            if self._fpointer in nid:
                self._fpointer.remove(nid)
        elif mode is self.INSERT:  # deprecate to ADD mode
            print("WARNNING: INSERT is deprecated to ADD mode")
            self.update_fpointer(nid)
dataset/ETHPy150Open caesar0301/treelib/treelib/node.py/Node.update_fpointer/swapped operands of `in`