    def load_state_dict(self, state_dict):
        """Load an LR scheduler state dict."""
        self.lr_scheduler.best = state_dict["best"]
        if "last_epoch" in state_dict:
            self.lr_scheduler.last_epoch = state_dict["last_epoch"]
Load an LR scheduler state dict.
fairseq/optim/lr_scheduler/reduce_lr_on_plateau.py