pip is a very convenient tool to install and manage python packages. However, I often experienced very slow download speeds. Sometimes I could not even connect, especially from China. The default behavior is to download packages from
pypi.org. This can be changed by specifying a mirror with the option
pip install <packages...> -i https://example-of-mirror.com/simple
Using a mirror that is closer to your city can increase the download speed. The following list of mirrors is suitable for China:
Now, enjoy decent install speeds!