1.mac默认已安装有python和easy_install
2.进入终端，使用root的权限，然后输入，回车后需要root的密码，即可安装成功，成功结果如下所示
sudo easy_install selenium
Downloading https://pypi.python.org/packages/source/s/selenium/selenium-2.46.0.tar.gz#md5=6db65e1e7653da0fdc514df5db76d662
Processing selenium-2.46.0.tar.gz
Writing /tmp/easy_install-prooMD/selenium-2.46.0/setup.cfg
Running selenium-2.46.0/setup.py -q bdist_egg --dist-dir /tmp/easy_install-prooMD/selenium-2.46.0/egg-dist-tmp-ERjNhl
Adding selenium 2.46.0 to easy-install.pth file
Installed /Library/Python/2.7/site-packages/selenium-2.46.0-py2.7.egg
Processing dependencies for selenium
Finished processing dependencies for selenium