    def step_update(self, num_updates):
        """Update the learning rate after each update."""
        if self.cfg.warmup_updates > 0 and num_updates < self.cfg.warmup_updates:
            self.warmup_factor = (num_updates + 1) / float(self.cfg.warmup_updates)
            self.optimizer.set_lr(self.warmup_factor * self.lr)
        else:
            self.optimizer.set_lr(self.lr)
        return self.optimizer.get_lr()
Update the learning rate after each update.
fairseq/optim/lr_scheduler/fixed_schedule.py