invalid type, must be a string or Tensor [TensorFlow]

Question

I have problem in Machine Learning library from Google - Tensorflow. When I want to initialize my session, it tells me that must be string or tensor. I did not spot any mistake.

import tensorflow as tf
from tensorflow.examples.tutorials.mnist import input_data
mnist = input_data.read_data_sets('MNIST_data', one_hot=True)

sess = tf.InteractiveSession()

x = tf.placeholder(tf.float32, shape=[None, 784])
y_ = tf.placeholder(tf.float32, shape=[None, 10])

W = tf.Variable(tf.zeros([784,10]))
b = tf.Variable(tf.zeros([10]))

sess.run(tf.initialize_all_variables)

y = tf.nn.softmax(tf.matmul(x,W) + b)

cross_entropy = tf.reduce_mean(-tf.reduce_sum(y_ * tf.log(y), reduction_indices=[1]))

train_step = tf.train.GradientDescentOptimizer(0.5).minimize(cross_entropy)

for i in range(1000):
    batch = mnist.train.next_batch(50)
    train_step.run(feed_dict={x: batch[0], y_: batch[1]})

correct_prediction = tf.equal(tf.argmax(y,1), tf.argmax(y_,1))
accuracy = tf.reduce_mean(tf.cast(correct_prediction, tf.float32))

print accuracy.eval(feed_dict={x: mnist.test.images, y_: mnist.test.labels})

This is output of the following program in terminal:

(tensorflow) juldou-box@juldou-box:~/tensorflow$ python mnist_e.py 
Extracting MNIST_data/train-images-idx3-ubyte.gz
Extracting MNIST_data/train-labels-idx1-ubyte.gz
Extracting MNIST_data/t10k-images-idx3-ubyte.gz
Extracting MNIST_data/t10k-labels-idx1-ubyte.gz
Traceback (most recent call last):
  File "mnist_e.py", line 13, in <module>
    sess.run(tf.initialize_all_variables)
  File "/home/juldou-box/tensorflow/local/lib/python2.7/site-packages/tensorflow/python/client/session.py", line 372, in run
    run_metadata_ptr)
  File "/home/juldou-box/tensorflow/local/lib/python2.7/site-packages/tensorflow/python/client/session.py", line 584, in _run
    processed_fetches = self._process_fetches(fetches)
  File "/home/juldou-box/tensorflow/local/lib/python2.7/site-packages/tensorflow/python/client/session.py", line 540, in _process_fetches
    % (subfetch, fetch, type(subfetch), str(e)))
TypeError: Fetch argument <function initialize_all_variables at 0x7fe4ca157c80> of <function initialize_all_variables at 0x7fe4ca157c80> has invalid type <type 'function'>, must be a string or Tensor. (Can not convert a function into a Tensor or Operation.)

Answer 1

I think you just missed a pair of parentheses () after tf.initialize_all_variables ;)

As python says, it's in line 13, look after

sess.run(tf.initialize_all_variables)