I recently 'upgraded' to MacOS Sierra (Apple's latest Operating System) by doing a clean install. This resulted in a couple of challenges, including some software that could not be installed, and for which I had to find some alternatives.
Another issue I ran into is that some Python3 scripts with matplotlib wouldn't run, because matplotlib wouldn't install correctly.
I could 'pip' all I wanted, but the result was always:
$ pip3 install matplotlib [...] The following required packages can not be built: freetype
Some googling pointed me to some articles that freetype is/was a part of the XQuartz (X11) software that's no longer (pre)installed on MacOS Sierra. And in the past I have always upgraded my OS. The times that I did a clean install on this machine.... Must have been ages ago.
After some frustrating hours of trying to get this 'freetype' thing installed, I ran into an article on yantonov.com which solved my issue finally.
First I installed 'homebrew'.
$ /usr/bin/ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)"
After that I installed pkg-config and freetype:
$ brew install pkg-config [...] $ brew install freetype [...]
And finally, I was able to successfully install matplotlib:
$ pip3 install matplotlib