install_tensorflow() keeps overwriting virtualenv, making it impossible to install tensorflow and keras
Please check that which pip you are using to install keras. It is possible that your pip may be pip3( will find libraries for python 3.x), while pip2 aka pip (will find libraries for python 2.x).

Keras is supported in python 2.7:

Tensorflow also, they promote use of python 3.x, you can checkout this tow download 2.7 compatible whl. tensorflow 2.7



You can check the pip version by executing below cammand from terminal. 

pip --version


To find location of python/ pip use:

which pip
which python


I would personally suggest use python 3.6 and above. As for python 2.x and python 3.4, support is going to be end soon.