In some instances, pip can have problems trying to correctly detect the python version and so can cause problems.
So for Tensorflow, if you wish to use Python2, then use
export TF_BINARY_URL=https://storage.googleapis.com/tensorflow/linux/cpu/tensorflow-0.12.1-cp27-none-linux_x86_64.whl
sudo pip install --upgrade $TF_BINARY_URL
and for Python3:
export TF_BINARY_URL=https://storage.googleapis.com/tensorflow/linux/cpu/tensorflow-0.12.1-cp34-cp34m-linux_x86_64.whl
sudo pip3 install --upgrade $TF_BINARY_URL
More details available on Tensorflow's Download and Setup page
Also, as Tensorflow has a GUI outpit, check out this page: GUI based output