Mac使用brew安装Python时报错：Error: The following directories are not writable by your user:

今天在使用brew安装Python的时候出现这个错误，翻译过来大概意思是“你当前用户没有下列目录的写权限”
如下

Error: The following directories are not writable by your user:
/usr/local/lib/python3.7/site-packages

You should change the ownership of these directories to your user.
  sudo chown -R $(whoami) /usr/local/lib/python3.7/site-packages

And make sure that your user has write permission.
  chmod u+w /usr/local/lib/python3.7/site-packages

然后在网上百度，看到好多都是修改/usr/local/bin和/usr/local/share文件夹的权限，
可是，这两个文件夹我当前用户都有写权限

但还是抱着试一试的心态照着做了，可是，该报错还是报错
如下例（为了避免一些不必要的麻烦就对一些内容隐藏）

照着做了后，也无法安装，然后仔细看报错信息，

You should change the ownership of these directories to your user.
  sudo chown -R $(whoami) /usr/local/lib/python3.7/site-packages

And make sure that your user has write permission.
  chmod u+w /usr/local/lib/python3.7/site-packages

You should change the ownership of these directories to your user.
你应该修改这些目录的所有权为你当前用户
And make sure that your user has write permission.
并且确保你当前用户具有写权限

写的明明白白，并且还附上修改语句，为什么不仔细看错误提示？为什么？为什么？为什么？（这里要加粗警示）

然后直接使用给的两条语句，修改/usr/local/lib/python3.7/site-packages的所有权和权限，安装Python，成功