>> So, with the current patch users could still not use the py launcher from a virtual environment with scripts that are supposed to work under UNIX :(
> 
> Correct. That's not the problem this PEP is intended to solve. 

Granted :)

> Another PEP could be written to look at this, but I suspect it could be quite
> hard to balance the various issues involved. 

Well, changes to the launcher will not typically break any existing code, but constant changes in behaviour may still be a cause of confusion and be hard to explain, à la:

"since Python 3.5 the launcher supports virtual environments, but the details of this support differ between 3.5 and 3.6, e.g. in 3.5, scripts with a python3 shebang line will be executed by the system python3 independent of the virtual environment, but in 3.6 a virtual environment python3 interpreter will be used."

IMO it would be preferable to have all virtualenv related changes happening with one release.

> As a start, maybe the
> Python Windows installer should be writing a "python3.exe" as well as
> "python.exe" and venv should put that in the virtualenv. (That's
> certainly something that has been suggested in the past). That may be
> a simpler solution than adding yet more complexity and special cases
> to the launcher.
> 

As an alternative, virtualenv could be changed to create a pyvenv.cfg file with the interpreter version like pyvenv does. Seems pretty simple and unproblematic to me and it might actually be useful to know the interpreter version without running it in other places besides the launcher. What do the pypa devs think about this?