Unless you intend to (eventually) break your OS, system-wide packages should be installed with system-wide package managers. That is, dpkg/apt, rpm/yum, pacman,

Unless you intend to (eventually) break your OS, system-wide packages should be installed with system-wide package managers. That is, dpkg/apt, rpm/yum, pacman, emerge or similar. Failure to comply with this rule bites hard when you install some other package that uses Python and pulls dependency from OS repository that you had already installed from PyPI. That obviously fails due to files being already present (and probably from another egg's version) and you're probably already using this egg somewhere so you probably can't readily replace it. Manual clean-up of such mess isn't pretty nor fun. So, if you want a non-project-bound package (like ipython), do so with `pip install --user`. Otherwise, virtualenv is the tool. (Obviously, there are non-trivial exceptional cases where sudo pip is fine. I believe they're quite rare.)