pypa/virtualenv — pull request #445 by pfmoore (2013-06-24 11:12:02+00:00)
Title: Allow -p to take a Python version number (Windows only)

Add the option to use a Python version in the -p option (something like -p 2.7 or -p 3.3). This is only supported on Windows, where the registry is read to determine the installed versions.

Not currently available for Unix, as there's no evidence that it's needed (version-specific executables like python-2.7 are normally on $PATH).