环境：

macOS Catalina 

现象：

pip install --upgrade pip

遇到错误以下错误

Could not install packages due to an EnvironmentError: HTTPSConnectionPool(host='files.pythonhosted.org', port=443): Max retries exceeded with url: /packages/43/84/23ed6a1796480a6f1a2d38f2802901d078266bda38388954d01d3f2e821d/pip-20.1.1-py2.py3-none-any.whl (Caused by SSLError("Can't connect to HTTPS URL because the SSL module is not available.",))

可能原因：

安装python3，openssl升级到1.1

解决办法：

brew switch openssl 1.0.2s