Coexistence of Python 2.x and 3.x on same OS

[Edward Diener]

On 9/30/2012 3:38 PM, Andrew Berg wrote:
> On 2012.09.30 14:14, Edward Diener wrote:
>> The situation is so confusing on Windows, where the file associations,
>> registry entries, and other internal software which allows a given
>> Python release to work properly when invoking Python is so complicated,
>> that I have given up on trying to install more than one Python release
>> and finding a relaible, foolproof way of switching between them. So
>> although I would like to use the latest 3.x series on Windows I have
>> decide to stick with the latest 2.x series instead because much software
>> using Python does not support 3.x yet.
>
> http://www.python.org/dev/peps/pep-0397/
>
> Unix-based OSes should already obey the shebang line, and on Windows,
> there's py.exe in 3.3 that will launch the intended version based on
> that shebang line.

The problem with that is that one has to already being using 3.3 to use 
this facility. I was hoping for a solution which was backwards 
compatible with Python 2.x.

My thought is a program distributed by Python which finds the versions 
of Python on an OS, lets the end-user choose which version should be 
invoked when Python is invoked, and does whatever is necessary to make 
that version the default version.

> While I was using the alpha/beta versions of 3.3, I
> had no problems invoking either 3.2 or 3.3 with the shebang line on Windows.

That does not solve the problem for Python 2.x distributions.