When pip is installed on a system that has an OS Python install there is currently a problem where pip install foo will throw an error because it doesn't have file permissions. This causes people to instead run sudo pip install foo which globally installs to the system Python. This creates an issue where people are using pip to manage system level packages when they should likely be using the system package manager.

So my intention is that pip should default to --user however there are a few sticking points with this:

• How does this interact with Windows? Does this make sense there?
• How does this interact with altinstall'd Pythons? Specially such as are installed with tools like https://github.com/yyuu/pyenv
• What do we do for when people do invoke pip as root? Installing into /root/.local/ does not seem very useful.
• What does this mean for get-pip and the pypa install instructions?
• ~/.local/bin is not on many people's $PATH, is there anything that can be done about this?
• --user installs lack precedence to global easy_install'd packages, which can be quite unexpected.

There are a number of issues that are relevant here: #624 #1443 #1153 #1500 #1051

/cc @ncoghlan