Hi,
On Thu, 22 Dec 2016 15:01:44 +0100 Johannes Schauer <josch@debian.org> wrote:
> On Mon, 17 Oct 2016 07:20:43 +0800 Paul Wise <pabs@debian.org> wrote:
> > * Use python-apt to do the resolution and emit `apt install pkg=1.2.3` commands?
>
> I don't see a way to achieve this with python-apt. Even when manually iterating
> through the given dependency string and checking which package in the apt cache
> satisfies the dependency, the solution would not always be correct. Here is an
> example in which this approach would fail:
>
> Suppose there are the packages A, B, C and D. A depends on D and D conflicts
> with C. Now the wants the following resolved:
>
> 'A | B, C'
>
> With the algorithm sketched above, A and C would be picked for installation but
> the solution would be invalid because A and C conflict via D. To avoid this
> situation, the code has to traverse all dependency trees which would in turn
> lead to the implementation of a full-fledged resolver. Certainly this is not
> desired.
on IRC, juliank informed me that this approach is already implemented in
python-apt. Specifically, try to do:
$ python3 -c "import apt.debfile; a = apt.debfile.DebPackage(); a.satisfy_depends_str('nginx-light | apache2, nginx-full'); a.check(); print(a.required_changes)"
(['nginx-full'], [], [])
That result is clearly wrong because it failed to satisfy the first alternative
(nginx-light and nginx-full conflict).
On the other hand, if I hand the problem to the script I presented in my last
email, then I get a correct list including apache2 and nginx-full.
Thanks!
cheers, josch
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