Fonttools can be easily installed using Homebrew on MacOS, by running brew install fonttools.
You should also install the brotli extension (to compress WOFF 2.0) and zopfli (to better compress WOFF 1.0) using:
/usr/local/Cellar/fonttools/4.2.4/libexec/bin/pip install brotli
/usr/local/Cellar/fonttools/4.2.4/libexec/bin/pip install zopfli