How to downgrade tensorflow, multiple versions possible?

Pip allows to specify the version

pip install tensorflow==1.1

I discovered the joy of anaconda: https://www.continuum.io/downloads. It allows multiple virtual environments to host different versions of phyton and tensorflow. For example the following creates a virtual environment with pyton3.5 and tensorflow1.1

C:> conda create -n tensorflow1.1 python=3.5
C:> activate tensorflow1.1
(tensorflow1.1) 
C:> pip install --ignore-installed --upgrade https://storage.googleapis.com/tensorflow/windows/gpu/tensorflow_gpu-1.1.0-cp35-cp35m-win_amd64.whl

voila, a virtual environment is created.

Is it possible to have multiple version of tensorflow on the same OS?

Yes, you can use python virtual environments for this. From the docs:

A Virtual Environment is a tool to keep the dependencies required by different projects in separate places, by creating virtual Python environments for them. It solves the “Project X depends on version 1.x but, Project Y needs 4.x” dilemma, and keeps your global site-packages directory clean and manageable.

After you have install virtualenv (see the docs), you can create a virtual environment for the tutorial and install the tensorflow version you need in it:

PATH_TO_PYTHON=/usr/bin/python3.5
virtualenv -p $PATH_TO_PYTHON my_tutorial_env 
source my_tutorial_env/bin/activate # this activates your new environment
pip install tensorflow==1.1

PATH_TO_PYTHON should point to where python is installed on your system. When you want to use the other version of tensorflow execute:

deactivate my_tutorial_env

Now you can work again with the tensorflow version that was already installed on your system.

If you are using python3 on windows then you might do this as well

pip3 install tensorflow==1.4

you may select any version from "(from versions: 1.2.0rc2, 1.2.0, 1.2.1, 1.3.0rc0, 1.3.0rc1, 1.3.0rc2, 1.3.0, 1.4.0rc0, 1.4.0rc1, 1.4.0, 1.5.0rc0, 1.5.0rc1, 1.5.0, 1.5.1, 1.6.0rc0, 1.6.0rc1, 1.6.0, 1.7.0rc0, 1.7.0rc1, 1.7.0)"

I did this when I wanted to downgrade from 1.7 to 1.4