解决 AttributeError: RefVariable object has no attribute _id（tf 版本低）

运行backpropagation.py，寻找 最小loss的代码 ```python import tensorflow as tf w = tf.Variable(tf.constant(5, dtype=tf.float32)) lr = 0.2 epoch = 40 for epoch in range(epoch):  # for epoch 定义顶层循环，表示对数据集循环epoch次，

>>阅读原文<<