Move iterator position forward

def next(self):
        """Move iterator position forward"""
        batch = mx.nd.zeros((self.batch_size, self.size[1], self.size[0], 3))
        i = self.cur
        for i in range(self.cur, min(len(self.list), self.cur+self.batch_size)):
            str_img = open(self.root+self.list[i]+'.jpg').read()
            img = imdecode(str_img, 1)
            img, _ = random_crop(img, self.size)
            batch[i - self.cur] = img
        batch = mx.nd.transpose(batch, axes=(0, 3, 1, 2))
        ret = mx.io.DataBatch(data=[batch],
                              label=[],
                              pad=self.batch_size-(i-self.cur),
                              index=None)
        self.cur = i
        return ret