1.mac系統本身帶有Python2.7，想要安裝Python3.5，需自行下載並安裝
安裝Python3.5后，需要安裝pip 和setup
2.安裝好pip后安裝selenium，具體命令如下：
pip3 install -U selenium
總是報錯，具體信息如下：
Could not fetch URL https://pypi.python.org/simple/selenium/: There was a problem confirming the ssl certificate: [SSL: TLSV1_ALERT_PROTOCOL_VERSION] tlsv1 alert protocol version (_ssl.c:646) - skipping
Could not find a version that satisfies the requirement selenium (from versions: )
No matching distribution found for selenium
You are using pip version 9.0.1, however version 10.0.1 is available.
You should consider upgrading via the 'pip install --upgrade pip' command.
根據信息提示，需要升級pip, 命令如下
pip install --upgrade pip
依然報錯，具體如下：
Could not fetch URL https://pypi.python.org/simple/pip/: There was a problem confirming the ssl certificate: [SSL: TLSV1_ALERT_PROTOCOL_VERSION] tlsv1 alert protocol version (_ssl.c:646) - skipping
3.解決方法：網絡上看了很多貼紙，最后翻牆發現使用curl來升級pip,命令如下：
curl https://bootstrap.pypa.io/get-pip.py | python3
等待下載完成就可以了，perfect！
再輸入安裝selenium的命令，即可成功。
pip3 install -U selenium
截圖如下：
總結：Python下下載相應的庫時，提示驗證ssh證書是否正確時，使用“curl https://bootstrap.pypa.io/get-pip.py | python3”升級pip，然后再下載安裝即可成功。