title: No backports error while retraining Tensorflow's Inception v3 model
body: <p>I have been trying to retrain Inception by following the tutorial here:
  <a href="https://www.tensorflow.org/tutorials/image_retraining" rel="nofollow noreferrer">https://www.tensorflow.org/tutorials/image_retraining</a>.
  I get this error "No module named backports"
  when I run this</p>
  
  <pre><code>bazel-bin/tensorflow/examples/image_retraining/retrain --image_dir ~/marine_animal_species1
  </code></pre>
  
  <p>This is the full Traceback:</p>
  
  <pre><code>Traceback (most recent call last):
  
        File "/home/karthik/tensorflow/bazel-bin/tensorflow/examples/image_retraining/retrain.runfiles/org_tensorflow/tensorflow/examples/image_retraining/retrain.py", line 91, in &lt;module&gt;
          import tensorflow as tf
        File "/home/karthik/tensorflow/bazel-bin/tensorflow/examples/image_retraining/retrain.runfiles/org_tensorflow/tensorflow/__init__.py", line 24, in &lt;module&gt;
          from tensorflow.python import *
        File "/home/karthik/tensorflow/bazel-bin/tensorflow/examples/image_retraining/retrain.runfiles/org_tensorflow/tensorflow/python/__init__.py", line 64, in &lt;module&gt;
          from tensorflow.python.framework.framework_lib import *
        File "/home/karthik/tensorflow/bazel-bin/tensorflow/examples/image_retraining/retrain.runfiles/org_tensorflow/tensorflow/python/framework/framework_lib.py", line 100, in &lt;module&gt;
          from tensorflow.python.framework.subscribe import subscribe
        File "/home/karthik/tensorflow/bazel-bin/tensorflow/examples/image_retraining/retrain.runfiles/org_tensorflow/tensorflow/python/framework/subscribe.py", line 26, in &lt;module&gt;
          from tensorflow.python.ops import variables
        File "/home/karthik/tensorflow/bazel-bin/tensorflow/examples/image_retraining/retrain.runfiles/org_tensorflow/tensorflow/python/ops/variables.py", line 26, in &lt;module&gt;
          from tensorflow.python.ops import control_flow_ops
        File "/home/karthik/tensorflow/bazel-bin/tensorflow/examples/image_retraining/retrain.runfiles/org_tensorflow/tensorflow/python/ops/control_flow_ops.py", line 70, in &lt;module&gt;
          from tensorflow.python.ops import tensor_array_ops
        File "/home/karthik/tensorflow/bazel-bin/tensorflow/examples/image_retraining/retrain.runfiles/org_tensorflow/tensorflow/python/ops/tensor_array_ops.py", line 33, in &lt;module&gt;
          from tensorflow.python.util import tf_should_use
        File "/home/karthik/tensorflow/bazel-bin/tensorflow/examples/image_retraining/retrain.runfiles/org_tensorflow/tensorflow/python/util/tf_should_use.py", line 28, in &lt;module&gt;
          from backports import weakref  # pylint: disable=g-bad-import-order
      ImportError: No module named backports
  </code></pre>
  
  <p>I use ubuntu 16.04.
  Thank you for the help.</p>