pip安装依赖的时候报错，pg_config executable not found, 所以需要在mac上安装postgresql。
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brew install postgresql
如果出现Updating Homebrew并且卡住了，请参考
安装过程中，有可能会遇到操作文件权限不够的情况，添加一下权限就可以了。
安装成功，将有如下提示：
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To migrate existing data from a previous major version of PostgreSQL run: brew postgresql-upgrade-database
To have launchd start postgresql now and restart at login: brew services start postgresql Or, if you don't want/need a background service you can just run: pg_ctl -D /usr/local/var/postgres start ==> Summary 🍺 /usr/local/Cellar/postgresql/11.5_1: 3,189 files, 35.6MB ==> `brew cleanup` has not been run in 30 days, running now... Pruned 4 symbolic links and 58 directories from /usr/local