Since you can not easily install Steem-Python on a stock Ubuntu 16.40 anymore, I switched to Ubuntu 17.10, which comes with the required Python 3.6 or higher.
The installation was not as smooth as I had wished for.
This is what it says in the repository:
Installation
You can install steem-python with pip:
pip install -U steem
Source: https://github.com/steemit/steem-python
On a fresh Ubuntu 17.10 this will not work at all.
Anyways, you want to actually do this:
pip3 install -U steem
But for that to work, you need the following:
sudo apt install python3-pip
pip3 install setuptools
pip3 install scrypt
pip3 install wheel
pip3 install pytest
sudo apt-get install libssl-dev
Now you can install Steem-Python:
pip3 install steem
I hope I could save someone some time, because figuring this out took me longer than I would like to admit.