py新手提问，例子报错，是否是我的环境问题

Question

py3.5环境，运行例子程序

```import tensorflow as tf
w1=tf.Variable(tf.random_normal([2,3], stddev=1))
w2=tf.Variable(tf.random_normal([3,1], stddev=1))
x=tf.placeholder(tf.float32,shape=(3,2),name="input")
a=tf.matmul(x,w1)
y=tf.matmul(a,w2)
sess=tf.Session()
init_op=tf.initialize_all_variables
sess.run(init_op)
sess.run(y,feed_dict={x: [[0.7,0.9], [0.1,0.4], [0.5,0.8]]})

这个是书上的例子，但是运行后报如下错误
TypeError: Fetch argument <function should_use_result.<locals>.wrapped at 0x000002B496D16AE8> has invalid type <class 'function'>, must be a string or Tensor. (Can not convert a function into a Tensor or Operation.)
请教各位是什么回事呢

Answer 1

init_op=tf.initialize_all_variables()，再试试