command line update of python3
You can easily switch versions of Python using pyenv.

For example (using Homebrew):

$ brew update
$ brew install pyenv
$ echo 'eval "$(pyenv init -)"' &gt;&gt; ~/.bash_profile

$ exec $SHELL

$ pyenv install 2.7.12
$ pyenv install 3.5.2
$ pyenv global 2.7.12 3.5.2

$ python -V
Python 2.7.12

$ python2 -V
Python 2.7.12

$ python2.7 -V
Python 2.7.12

$ python3 -V
Python 3.5.2

$ python3.5 -V
Python 3.5.2