@Jens Lindgren

I know, pretty annoying right? But see previous answer by Paul here http://bugs.python.org/issue28686#msg287181

> The Unix ability to have 2 different versions of Python on PATH 
> and select which you use based on executable name doesn't exist 
> on Windows, and so there's no equivalent of the 
> Unix "#!/usr/bin/env pythonX[.Y]"

Now if you ask me, I would expect py.exe to handle all common types of shebang you may find in the wild. 
But I assume that the correct answer instead is that "#!/usr/bin/env pythonX[.Y]" is not a portable shebang, and you just should stop using it. If you happen to find such a shebang in someone else's script, file a bug report there.