Tensorflow,assign value to variable

Question

I am total newbie to tensorflow, I am learning from

https://www.tensorflow.org/get_started/get_started

fixW = tf.assign(W, [-1.])

works fine,but

fixb = tf.assign(b, [1.])
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/milenko/anaconda3/lib/python3.6/site-packages/tensorflow/python/ops/state_ops.py", line 272, in assign
    return ref.assign(value)
AttributeError: 'Tensor' object has no attribute 'assign'

One other example

zero_tsr = tf.zeros([1.,2.])
zero_tsr
<tf.Tensor 'zeros:0' shape=(1, 2) dtype=float32>

If I try to change zero_tsr

fixz = tf.assign(zero_tsr, [2.,2.])
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/milenko/anaconda3/lib/python3.6/site-packages/tensorflow/python/ops/state_ops.py", line 272, in assign
    return ref.assign(value)
AttributeError: 'Tensor' object has no attribute 'assign'

Again,the same problem.

I have not changed shell,everything is the same.Why do I have problem here?

Answer 1

In the example you posted:

zero_tsr = tf.zeros([1.,2.])
zero_tsr
<tf.Tensor 'zeros:0' shape=(1, 2) dtype=float32>

zero_tsr is a constant and not a variable, so you cannot assign a value to it.

From the documentation:

assign( ref, value, validate_shape=None, use_locking=None, name=None )

ref: A mutable Tensor. Should be from a Variable node. May be uninitialized.

For example, this will work fine:

import tensorflow as tf
zero_tsr = tf.Variable([0,0])
tf.assign(zero_tsr,[4,5])

while this code will raise an error

import tensorflow as tf
zero_tsr = tf.zeros([1,2])
tf.assign(zero_tsr,[4,5])

The error that is raised is exactly the error you posted:

AttributeError: 'Tensor' object has no attribute 'assign'