Under Windows, CPython is shipped with a very useful py command.
PEP-397 describes in details its behaviour, and its C implementation can be found in the CPYthon Mercurial repository.
There has already been a lenghty discussion in the "python-ideas" mailing list to write a Linux equivalent. I agree with what Éric Araujo wrote, that there isn't really a need for such a tool under Linux.
But I find it useful to use a py -3.4 -m pip install $pkg or py 27 $file shorthand, and hence I wrote a basic bash script equivalent : https://github.com/Lucas-C/linux_configuration/blob/master/bin/py
EDIT [2018/06/18]: there is also Brett Cannon python-launcher written in Rust
