How to find which version of TensorFlow is installed in my system?

This depends on how you installed TensorFlow. I am going to use the same headings used by TensorFlow's installation instructions to structure this answer.

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Pip installation

Run:

python -c 'import tensorflow as tf; print(tf.__version__)'  # for Python 2
python3 -c 'import tensorflow as tf; print(tf.__version__)'  # for Python 3

Note that python is symlinked to /usr/bin/python3 in some Linux distributions, so use python instead of python3 in these cases.

pip list | grep tensorflow for Python 2 or pip3 list | grep tensorflow for Python 3 will also show the version of Tensorflow installed.

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Virtualenv installation

Run:

python -c 'import tensorflow as tf; print(tf.__version__)'  # for both Python 2 and Python 3

pip list | grep tensorflow will also show the version of Tensorflow installed.

For example, I have installed TensorFlow 0.9.0 in a virtualenv for Python 3. So, I get:

$ python -c 'import tensorflow as tf; print(tf.__version__)'
0.9.0

$ pip list | grep tensorflow
tensorflow (0.9.0)

Almost every normal package in python assigns the variable .__version__ to the current version. So if you want to find the version of some package you can do the following

import a
a.__version__

For tensorflow it will be

import tensorflow as tf
tf.version.VERSION

For old versions of tensorflow (below 0.10), use tf.__version__

If you have installed via pip, just run the following

$ pip show tensorflow
Name: tensorflow
Version: 1.5.0
Summary: TensorFlow helps the tensors flow