$ sudo pip install
Installs the package globally in your python installation, i.e. for all users.
$ pip install --user
Installs to the local user directory, i.e. ~/.local/lib/python — just you.
Example:
$ sudo pip install jupyter
$ jupyter notebook
Will run jupyter, open a web browser, allow you to work with notebooks.
$ pip install --user jupyter
$ jupyter notebook
Will do nothing until your local directory has been added to your PATH.
There was recently malicious code included in pypi. Never use sudo to install with pip. This is the same as running a virus as root. Either add your local folder to your PATH or use a virtualenv.