tensorflow is currently (2nd hald of 2018 until ???) 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
Python 2.7 is still available, and tensorflow will work in that environment. has already been installed in a central location, so if python 2 is an option for you, you can use it.
Probably the mbest 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.
or for bash:
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.