What is the purpose of "pip install --user ..."?
pip defaults to installing Python packages to a system directory (such as /usr/local/lib/python3.4). This requires root access.
--user makes pip install packages in your home directory instead, which doesn't require any special privileges.
--user installs in site.USER_SITE.
For my case, it was /Users/.../Library/Python/2.7/bin. So I have added that to my PATH (in ~/.bash_profile file):
export PATH=$PATH:/Users/.../Library/Python/2.7/bin
Just a warning:
According to this issue, --user is currently not valid inside a virtual env's pip, since a user location doesn't really make sense for a virtual environment.
So do not use pip install --user some_pkg inside a virtual environment, otherwise, virtual environment's pip will be confused. See this answer for more details.