This answer almost answers my question too, but needs example of $PATH for a novice
Mac OS Terminal在“ pip3安装”中显示此结果...
Installing collected packages: fontTools, ufoLib, ufonormalizer, defcon, pyclipper, booleanOperations, psautohint, fontMath, mutatorMath, fontPens, afdko
fonttools,pyftinspect,pyftmerge,pyftsubset和ttx脚本安装在“ /Users/adrianshome/Library/Python/3.7/bin”中,该文件不在PATH上。