There shouldn't be a "python install" at all, let alone a "default". Whether an application uses this-or-that Python interpreter, or Ruby/Bash/Scheme/whatever s

There shouldn't be a "python install" at all, let alone a "default". Whether an application uses this-or-that Python interpreter, or Ruby/Bash/Scheme/whatever should make about as much difference as whether a C program was compiled with GCC or Clang: it's an implementation detail, which doesn't need to be co-ordinated with everything else on the OS (although the package maintainers may want to coordinate, e.g. to allow re-use of files via soft-/hard-links, bind-mounts, etc.). When I "install foo-1.0 into my python environment", that's an annoying implementation detail (which is also imperative and non-atomic, i.e. there is a time where the python environment exists without foo-1.0). What I really want is "run a 'python' command where 'import foo' will have foo-1.0". That shouldn't break other applications which just-so-happen to use foo-0.5, or whatever.