If you install python via the package manager for your OS (brew, apt-get, yum) you can have only one version of python at the same time.

At best one python2 and one python3

But if you want to have (and want ability to easily switch between) say 3.5.2 and 3.6.0 (and 2.7.2) then you should definitely consider using pyenv

pyenv is not platform specific. It installs all the versions in your home directory under ~/.pyenv

Some useful commands:

pyenv versions  # Lists the various versions on your system
pyenv install -l # Lists available versions you can install
pyenv install 2.7.0 # Install Python 2.7.0

Off course there is lot more on the pyenv page

There is a pyenv plugin that helps manager virual environments. See here