alias py="/opt/python3.4/bin/python3"

map <F9> :call SpecialCompileRun()<CR>
func! SpecialCompileRun()
    exec "w"
    if &filetype == 'python'
        exec '!time py %'
    endif
endfunc

...
exec '!time ' . $PY . ' %'
...

sudo ln -s /opt/python3.4/bin/python3 /usr/bin/py