Mac 下安装Python3.5出现“python3-3.5.0 already installed, it's just not linked”错误

Error: An unexpected error occurred during the `brew link` step
The formula built, but is not symlinked into /usr/local
Permission denied - /usr/local/Frameworks
Error: Permission denied - /usr/local/Frameworks

brew install python3
Warning: python3-3.5.0 already installed, it's just not linked

**Please note that these warnings are just used to help the Homebrew maintainers**
**with debugging if you file an issue. If everything you use Homebrew for is**
**working fine: please don't worry and just ignore them. Thanks!**

Warning: The /usr/local is not writable.

You should probably change the ownership and permissions of /usr/local
back to your user account.
  sudo chown -R $(whoami) /usr/local

Warning: The /usr/local directory is not writable.
Even if this directory was writable when you installed Homebrew, other
software may change permissions on this directory. Some versions of the
"InstantOn" component of Airfoil are known to do this.

You should probably change the ownership and permissions of /usr/local
back to your user account.
  sudo chown -R $(whoami):admin /usr/local