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[Python-Dev] Python install layout and the PATH on win32

VanL van.lindberg at gmail.com
Tue Mar 20 20:22:55 CET 2012 
On 3/20/2012 1:56 PM, Paul Moore wrote:
>  This is covered (better, IMO) by PEP 397 - Python Launcher for
>  Windows. Step 2, just run "py". If you prefer a particular version,
>  run "py -2" or "py -3" or "py -3.2".

Interesting. I haven't played around with that at all, so can't comment. 
I will have to try it out.

>  Adding python.exe to PATH actually makes this message *worse* as it
>  confuses the issue. In a post-PEP 397 world, I would say that we
>  should be telling Windows users *not* to run python.exe at all.
>  (Unless they are using virtualenvs - maybe PEP 397 could do with an
>  extra option to run the Python from the currently active virtualenv,
>  but that's a side issue).

I think that having the PATH manipulation be optional might address this 
issue. I also think that the PEP 397 launcher should respect virtualenvs 
- at least the built-in pyvenvs - or else there will be lots of confusion.


>  For your steps 3 and 4, there is certainly user intervention
>  required as things stand. It would indeed be nice if "regetron" just
>  worked as expected. But I'd argue a few points here:
>
>  1. On Windows, if regetron was not explicitly an application for
>  working with my Python installation (like pip, easy_install, nose,
>  etc) then I'd prefer it to be packaged as a standalone application
>  using cx_Freeze or py2exe. I've had too many "applications" break
>  because I accidentally uninstalled a dependency from my Python
>  installation to want anything that is an end-user application
>  installed into my Python scripts/bin directory.

Maybe so - and I would probably agree that for any packaged application, 
bundling it into its own environment (or at least its own virtualenv) is 
the best practice. But what about pip, easy_install, nose, cython, 
pygments, PIL, etc, that do this and are meant to be associated with a 
particular python version? Substitute "nose" for "regetron" if you want, 
and there is still a problem.

>  The problem with your example is that it depends on the
>  package/executable. I looked at regetron (I thought it was a made up
>  example at first!)

...! I got the name from the feedback I received. I thought it was made 
up too.

>  I have no idea what proportion of Python users on Windows have
>  multiple versions installed. I also have no idea how many such users
>  work on the command line. My guess would be "not that many" and "not
>  that many of the first group" respectively... But there are big
>  groups like scientists and web developers who could sway these
>  figures a lot.

There are a number of casual users that probably only have one version 
installed, but every python user/dev on windows that I know has one 
python that they consider to be "python," and everything else needs to 
be launched with a suffix (e.g., python26.exe). This is usually put 
earlier on the PATH so that it gets picked up first. For example, right 
now I have 2.6, 2.7, 3.2, jython, and pypy all installed, and I have 
"python" pointing to 2.7.

>  I'd be curious as to how much PEP 397's py.exe would have helped
>  those people. But yes, it's an issue. Although someone at some point
>  will have to introduce those beginners to the question of Python 2 vs
>  Python 3, and PATH pain will hit them then, anyway.

I would imagine that it would help steps 1 and 2, but 3 and 4 would be 
problematic (how can you pip install something using py?) unless you 
were in a virtualenv, and then (unless py respected the virtualenv) the 
whole thing would be problematic, because there wouldn't be one clear 
way to do it.
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