Citing Marcus Smith (maintainer of pip):
If you think the global site is out of date, and want the latest in the user site, then use:
`pip install --upgrade --user SomePackage`
If the global site is up to date, and you really just want the same thing duplicated in --user, then use:
`pip install --ignore-installed --user SomePackage`
(which works correctly now after the merge of #1352, which is to be released in v1.5)
How can I make pip install --user always go to ~/.local and not a system-wide directory?
Use both --upgrade and --ignore-installed arguments.
Source: <https://stackoverflow.com/a/20304268/162264>