When installing a package using pip, I get the following message:

Obtaining some-package from git+git://github.com/some-user/some-package.git@commit-hash#egg=some_package-dev (from -r requirements.txt
 (line 3))
  git clone in /Users/me/Development/some-env/src/some-package exists with
 URL https://github.com/some-user/some-package.git
  The plan is to install the git repository git://github.com/some-user/some-package.git
What to do?  (s)witch, (i)gnore, (w)ipe, (b)ackup

I see that this particular case is probably caused by a change of protocol in URL (new requirement uses git://, while the one already installed uses https://).

However, I wonder what exactly happens if I choose either of the choices (switch, ignore, wipe, backup). I'm unable to find an explanation in pip documentation.

A patch explaining this option was merged into the PIP documentation, but it was not released until Pip 6.0 (2014-12-22). (https://github.com/pypa/pip/commit/b5e54fc61c06268c131f1fad3bb4471e8c37bb25). Here is what that patch says:

--exists-action option

This option specifies default behavior when path already exists. Possible cases: downloading files or checking out repositories for installation, creating archives. If --exists-action is not defined, pip will prompt when decision is needed.

• (s)witch

  Only relevant to VCS checkout. Attempt to switch the checkout to the appropriate url and/or revision.

• (i)gnore

  Abort current operation (e.g. don't copy file, don't create archive, don't modify a checkout).

• (w)ipe

  Delete the file or VCS checkout before trying to create, download, or checkout a new one.

• (b)ackup

  Rename the file or checkout to {name}{'.bak' * n}, where n is some number of .bak extensions, such that the file didn't exist at some point. So the most recent backup will be the one with the largest number after .bak.

And here is a link to description of that option in the now-updated documentation: https://pip.pypa.io/en/stable/cli/pip/#exists-action-option.