[Distutils] Multi-version import support for wheel files

[Paul Moore]

On 25 August 2013 23:14, PJ Eby <pje at telecommunity.com> wrote:

> > Unless I'm missing something, I suspect that this over-counts the number
> of
> > people using multi-version, in the sense that many (the majority?) of
> > wrapper scripts using multi-version do not actually need to,because the
> > users never install more than one version. And quite likely don't even
> know
> > that they could.
>
> That's just it: if you install two programs, one of which needs
> CherryPy 2 and the other CherryPy 3, then with easy_install this just
> works, without you having any idea that you even have more than one
> version installed, unless you for some reason choose to look into it.
>
> Thus, you don't have to know you have multiple versions installed; it
> can trivially happen by way of dependencies you aren't paying
> attention to.  The more things you install, the more likely it is you
> have two versions hanging around.


OK, I see. But I'm not sure if we're agreeing or disagreeing over the
result. To me, this is a bad thing on the principle that there is a cost to
multiversion support (it's not part of core Python, so you have to do
*something* to make it work) and so having people inadvertently pay that
cost to use a feature that they don't actually *need* is wrong. An opt-in
solution is fine, as in that case the user has to choose to use
multiversion, and if they don't want to they can choose an alternative
approach that they accept the cost of (for example, running their one
CherryPy 2 using application in a virualenv).

One other point, just as a matter of curiosity (because it's not relevant
to the current discussion): in your explanation above, there doesn't seem
to be any step that says the user normally uses CherryPy 3 (so that would
be the one they would get automatically at the interactive interpreter).
For me, that's really the only use case I'd have for multi-versioning - 99%
of the time I use a particular version of a project, but I have one
particular application that can't work with the version I prefer.

Paul
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