"`Tensor` objects are not iterable when eager execution is not "

用tensorflow搭建卷积神经网络，使用yield来返回数据batch，然后输入到卷积神经网络训练，相关代码如下：

def generate_batch(batch_train_list, max_frame, size_x, size_y, batch_label):
    batch_rgb = get_rgb_batch(batch_train_list, max_frame, size_x, size_y)
    # 得到rgb特征 [video/batch_size,batch_size,max_frame,size_x,size_y,3],
    # size_x和size_y为图片大小，max_frame为每个视频抽取出的帧数，3为通道数
    batch_label = np.asarray(batch_label, dtype=np.int32)
    for i, j in zip(batch_rgb, batch_label):
        # 按batch返回
        yield i, j

train_label = tf.cast(tf.convert_to_tensor(train_label), dtype=tf.int32)
with tf.Session() as sess:
    sess.run(tf.global_variables_initializer())
    # step = 1000
    for i in range(1000):
        for xs, ys in tool.generate_batch(train_list,max_frame,size_x,size_y,train_label):
            sess.run(train_step, feed_dict={tf_X: xs, tf_Y: ys})

运行之后报错，报错处为：for xs, ys in tool.generate_batch(train_list,max_frame,size_x,size_y,train_la