解决报错Could not satisfy explicit device specification '' because the node was colocated with a group of nodes that required incompatible device '/device:GPU:0'

sess = tf.Session(config=tf.ConfigProto(log_device_placement=True))
改为如下：
sess = tf.Session(config=tf.ConfigProto(allow_soft_placement=True, log_device_placement=True))

备注：allow_soft_placement=True表示当没有GPU实现可用时，使用将允许TensorFlow回退到CPU。