multiple python versions

[Shlomo Solomon]

OK - to sum up:
1 - thanks to Omer and Dan
2 - it seems that I did understand the concept of virtual environments
- as I wrote in my original post:
> I know I can use venv to set up virtual environments for different
> versions, but although I haven't tried it, I don't see how that would
> solve the problem.
3 - based on the answers you both wrote, there's no solution to the
"problem" of having to re-install modules.
4 - and it's probably not a good idea to try :-)
5 - based on all of the above, I'll probably pass on the idea of using
2 versions and wait for Kubuntu to move to 3.9, which will probably not
be too far in the future. 

Again - thanks 



On Thu, 22 Jul 2021 20:07:20 +0300
Omer Zak <w1 at zak.co.il> wrote:

> FALSE ECONOMICS ALERT!
> FALSE ECONOMICS ALERT!
> FALSE ECONOMICS ALERT!
> 
> You say that "most modules DO work when moving to a newer version of
> Python".
> However when they do not work, it is a lot of work diagnosing the
> problem and finding which module needs to have both versions installed
> in parallel.
> 
> It is better to spend the (relatively short and predictable) time
> maintaining a full virtualenv for each project. And if you are short
> on disk space, then today's disks are big and inexpensive - much less
> expensive than the time you spend trying to save few megabytes by not
> installing parallel versions.
> 
> 
> 
> 
> On Thu, 2021-07-22 at 20:02 +0300, Shlomo Solomon wrote:
> > On Thu, 22 Jul 2021 19:50:46 +0300
> > Omer Zak <w1 at zak.co.il> wrote:
> > 
> > > Why do you want to avoid having to re-install modules for each
> > > version/environment?
> > > 
> > The short answer: too much work
> > 
> > The slightly longer answer: Although there are certainly changes
> > between versions of Python and/or modules, most modules DO work when
> > moving to a newer version of Python. I don't remember re-installing
> > everything when upgrading to a newer version of Python.
> > 
> > But here, my problem is not upgrading, but keeping both versions.
> > 
> > 
> > 
> > 
> > > In the general case, a module version is compatible only with a
> > > subset
> > > of Python versions, due to API changes from Python version to
> > > Python
> > > version.
> > > 
> > > You also want to let each project decide with which module version
> > > it
> > > wants to work, due to potential incompatibilities between module
> > > versions (it is no accident that pip freeze preserves installed
> > > module
> > > versions).
> > > 
> > > 
> > > On Thu, 2021-07-22 at 19:37 +0300, Shlomo Solomon wrote:
> > > > Omer Zak <w1 at zak.co.il> wrote:
> > > > > The answer to your prayers is pyenv.
> > > > > It allows you to install multiple Python versions in parallel,
> > > > > and
> > > > > for
> > > > > each version you can maintain several virtualenvs.
> > > > 
> > > > Dan Yasny <dyasny at gmail.com> wrote:
> > > > > How about using virtualenv for alternative versions?
> > > > 
> > > > Yes, I know about pyenv and virtualenv, but wouldn't I have to
> > > > re-install modules for each version/environment? That's what I'm
> > > > trying
> > > > to avoid.
> > 
> > 



-- 
Shlomo Solomon
http://the-solomons.net
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