We strongly recomend that Python 3 is used. That being said Python 2.7 is still usable with this workshops. None of the workshops exercises will be specific to a Python version.
Python.org provides a number of MSI downloads for Windos. You can get them here
Once the download is finished, run the MSI and follow the installer's instructions.
Mac OsX 10.8 and up has Python 2.7 installed out of the box. If you want to update or install a new Python version please read: Using Python on Macintosh
You could also install Python using a package manager sush as Homebrew.
Python 2.7.x
$> brew install python
Python 3.x
$> brew install python3
Most Linux distros already have a version of Python installed. To verify this you can type the following command: $> python --version
If by any chance you do not have Python installed you should use your distro's package manager to installed the desired Python version.