最新版的MacOS Sierra默认带的python环境仍然为2.7.10，本文将介绍使用Brew安装python3.5并做简单的配置，打造python2，python3共存的开发环境
直接尝试brew安装，提示需要执行brew link gdbm
thatsitdeMacBook-Pro:~ thatsit$ brew install python3
Updating Homebrew...
Error: You must `brew link gdbm` before python3 can be installed
thatsitdeMacBook-Pro:~ thatsit$
按提示执行brew link gdbm，提示目录权限问题
thatsitdeMacBook-Pro:~ thatsit$ brew link gdbm
Linking /usr/local/Cellar/gdbm/1.12...
Error: Could not symlink share/man/man3/gdbm.3
/usr/local/share/man/man3 is not writable.
thatsitdeMacBook-Pro:~ thatsit$
尝试sudo执行brew，提示已经不再支持以root权限执行
thatsitdeMacBook-Pro:~ thatsit$ sudo brew link gdbm
Password:
Error: Running Homebrew as root is extremely dangerous and no longer supported.
As Homebrew does not drop privileges on installation you would be giving all
build scripts full access to your system.
thatsitdeMacBook-Pro:~ thatsit$
确认目录权限并调整
thatsitdeMacBook-Pro:~ thatsit$ ll /usr/local/share/man/man3/
total 240
-rw-rw-r-- 1 root wheel 25111 1 12 2014 cdt.3
-rw-rw-r-- 1 root wheel 27894 1 12 2014 cgraph.3
-rw-rw-r-- 1 root wheel 1762 1 12 2014 expr.3
-rw-rw-r-- 1 root wheel 2103 1 12 2014 gvc.3
-rw-rw-r-- 1 root wheel 2966 1 12 2014 gvpr.3
-rw-rw-r-- 1 root wheel 9628 1 12 2014 pack.3
-rw-rw-r-- 1 root wheel 5386 1 12 2014 pathplan.3
-rw-rw-r-- 1 root wheel 15026 1 12 2014 tcldot.3tcl
-rw-rw-r-- 1 root wheel 7109 1 12 2014 tkspline.3tk
-rw-rw-r-- 1 root wheel 8157 1 12 2014 xdot.3
thatsitdeMacBook-Pro:~ thatsit$
thatsitdeMacBook-Pro:~ thatsit$ sudo chown -R thatsit /usr/local/share/man/man3/
thatsitdeMacBook-Pro:~ thatsit$
再次执行，OK
thatsitdeMacBook-Pro:~ thatsit$ brew link gdbm
Linking /usr/local/Cellar/gdbm/1.12... 12 symlinks created
thatsitdeMacBook-Pro:~ thatsit$
thatsitdeMacBook-Pro:~ thatsit$ brew install python3
==> Installing dependencies for python3: xz
==> Installing python3 dependency: xz
==> Downloading https://homebrew.bintray.com/bottles/xz-5.2.2.el_capitan.bottle.tar.gz
######################################################################## 100.0%
==> Pouring xz-5.2.2.el_capitan.bottle.tar.gz
Error: The `brew link` step did not complete successfully
The formula built, but is not symlinked into /usr/local
Could not symlink lib/pkgconfig/liblzma.pc
/usr/local/lib/pkgconfig is not writable. You can try again using:
brew link xz
==> Summary