[Distutils] Why I like eggs (or similar mechanisms) and my thoughts on future of buildout

[Nick Coghlan]

On 21 August 2016 at 05:46, Jim Fulton <jim at jimfulton.info> wrote:
> On Sat, Aug 20, 2016 at 3:02 PM, Nick Coghlan <ncoghlan at gmail.com> wrote:
>> > I have the impression that uninstalling things can be
>> > problematic, but maybe that's been fixed.
>>
>> Uninstallation is fine, as we *do* have a full file manifest after a
>> component has been installed.
>
> So, if package A and B install the same file, X, and then A is uninstalled,
> is X still there?  If then B is uninstalled, does X go away?  Does this
> machinery depend on whether X has the the same contents in A and B?

If A and B install to the same path, B will overwrite A's version, and
if either is uninstalled, they'll delete whichever version is
currently there. Since "the same path" in this case usually refers to
either a script or a Python module, the unhandled conflict is really
at install time - we'd want something closer to the RPM/deb style "A
file already exists at that destination, so we're not installing the
requested package at all", rather than a Windows-style reference
counting system.

As Daniel notes, this kind of check is actually already possible when
installing from a wheel file today, it just requires someone with the
roundtuits to add it to pip (perhaps via a new vendorable package for
working with Python installation metadata and detecting conflicts
between what's already installed and a wheel being considered for
installation).

Cheers,
Nick.

-- 
Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia