解决 pip ERROR: Could not install packages due to an OSError: Missing dependencies for SOCKS support.

0. 背景

安装 python 环境时出现下面问题：

$ pip install -r requirements.txt
Looking in indexes: https://mirror.baidu.com/pypi/simple/, http://mirrors.aliyun.com/pypi/simple/
ERROR: Could not install packages due to an OSError: Missing dependencies for SOCKS support.

WARNING: There was an error checking the latest version of pip.

这是系统缺少必要的SOCKS依赖项或环境变量中设置了SOCKS代理。

1. 查看配置

 pip config list
global.extra-index-url='http://mirrors.aliyun.com/pypi/simple/'
global.index-url=