This course and all of the sample solutions use Python 3.
You can download and install Python 3 using the releases provided by the CPython team here. Installation using the windows installer packages should be straightforward, but if required you can find further documentation on the installation process here.
You can download and install Python 3 on a Mac using the Python download page, and there are further instructions in the official documentation.
As an alternative, Homebrew is a package manager for Mac OSX that is very useful for installing scientific software and dependencies. You can see the official Homebrew page for installation instructions. Once Homebrew is installed you can install Python using
brew install python
Debian Linux, and Ubuntu 20.04 both ship with Python 3 pre-installed.
As with everything you do in Python, it is recommended that you work in a virtual
environment during this course. You can create a virtual environment in Python 3 using
the venv module
python3 -m venv env
This creates a directory env containing the virtual environment. You can then activate
this environment using
source env/bin/activate
Once your environment is activated, you can install the dependencies for this course
using pip
pip install numpy scipy matplotlib