使用pip来安装python包有时候安装起来会非常慢，因此需要换成国内的源来加速下载：
使用命令
以Torch为例：
pip install -i https://pypi.tuna.tsinghua.edu.cn/simple torch
常用的国内源
清华大学：Simple Index
中国科学技术大学：Simple Index
阿里云：Simple Index
豆瓣 ：Simple Index
华中理工大学：http://pypi.hustunique.com/
山东理工大学：http://pypi.sdutlinux.org/
若无法连接
WARNING: The repository located at pypi.doubanio.com is not a trusted or secure host and is being ignored. If this repository is available via HTTPS we recommend you use HTTPS instead, otherwise you may silence this warning and allow it anyway with '--trusted-host pypi.doubanio.com'. ERROR: Could not find a version that satisfies the requirement opencv-python (from versions: none) ERROR: No matching distribution found for opencv-python
可以将源中的http改为https
需要user
Could not install packages due to an EnvironmentError: [Errno 13] Permission denied: '/anaconda3/lib/python3.7/site-packages/llvmlite-0.28.0.dist-info' Consider using the --user option or check the permissions.
需要加上--user：pip install <module> 改为 pip install --user <module>
pip install --user -i https://pypi.tuna.tsinghua.edu.cn/simple torch
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