Unfortunately, tensorflow is currently (2nd half of 2018 until 2019) not available for python 3.7
Downgrading the system python version is not an option, since many other packages, desktop components and operating system utilities expect python 3.7
UPDATE: as of October 2019, it seems possible to install tensorflow in python 3.7. This will simplify the situation.
Python 2.7 is still available (for a short while), and tensorflow will work in that environment. It has already been installed in a central location, so if python 2 is an option for you, you can use it.
Probably the best solution is, to create a separate python environment using python 3.6.
python3.6 -m venv mypython36
here, mypython36 is the name you choose, which will become the directory name where it gets installed.
source mypython36/bin/activate.csh
or for bash:
source mypython36/bin/activate
this is the command to activate the environment. This step needs to be done every time you want to use this special python environment. Inside the environment, 'python' refers to the chosen version 3.6, and the same is true for utilities like 'pip'. So:
pip install tensorflow pip install keras pip install jupyter
will install these packages into the newly created environment.