def _unpack_changed(self, name, old, new):
        # unpacker is not checked - it is assumed to be 
        if not isinstance(new, collections.Callable):
            raise TypeError(type(new)%"unpacker must be callable, not %s")
dataset/ETHPy150Open ipython/ipython-py3k/IPython/zmq/session.py/Session._unpack_changed/swapped operands of `%`