Working with different versions of GCC or Python using MacPorts

Browse to the MacPorts website.
Download the DMG image for your operating system
Open up a terminal Applications > Utilities > Terminal
Make sure that you have the latest version by running the self-update via the terminal command:
```
sudo port -v selfupdate
```

Install GCC or Python via the terminal command

sudo port install gcc5 
sudo port install gcc6
sudo port install gcc12 
sudo port install python311

First, identify which versions are installed on your system.
```
port select --list gcc
port select --list python
```
To make the version of gcc or python the default (i.e. the version you get when you run python or gfortran), run:
```
sudo port select --set gcc gcc12
sudo port select --set python python311
```