class CycleLR:
    def __init__(self, warm_epoch, all_epoch, target_lr, iters_epoch, period=4):
        self.iter = -1
        self.warmIters = iters_epoch * warm_epoch
        self.target_lr = target_lr
        self.step_iters = (all_epoch - warm_epoch) // period * iters_epoch

    def step(self):
        self.iter += 1
        if self.iter <= self.warmIters:
            lr = self.warm()
        else:
            cur_iter = (self.iter - self.warmIters) % self.step_iters
            lr = self.cosine(cur_iter)
        return lr

    def warm(self):
        return self.iter / self.warmIters * self.target_lr

    def cosine(self, cur_iter):
        lr = self.target_lr * (1 + np.cos(np.pi * cur_iter / self.step_iters)) * 0.5
        return lr