<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def set_npe(self, npe):
 """ Sets the NPE model. :params npe: NPE model string (e.g. "npe-200") NPE models are npe-100, npe-150, npe-175, npe-200, npe-225, npe-300, npe-400 and npe-g2 (PowerPC c7200 only) """


        if (yield from self.is_running()):
            raise DynamipsError("Cannot change NPE on running router")

        yield from self._hypervisor.send('c7200 set_npe "{name}" {npe}'.format(name=self._name, npe=npe))

        log.info('Router "{name}" [{id}]: NPE updated from {old_npe} to {new_npe}'.format(name=self._name,
                                                                                          id=self._id,
                                                                                          old_npe=self._npe,
                                                                                          new_npe=npe))
        self._npe = npe