I played with `withPackages` and it's rather nice. The only problem I had was "collision between A and B" style errors. Is there any plan to allow for collisions?
On 2 November 2016 at 06:05, Dmitry Kalinkin <[email protected]> wrote: > > > On 01 Nov 2016, at 11:56, Freddy Rietdijk <[email protected]> > wrote: > > > > > > > To solve 2) you could also make a wrapper that combines selected > outputs of the multiple output package without python itself. I think, this > is what texlive does. That way all the burden of wrapping will be limited > only to the multiple output packages. > > > > I'm not sure whether I understand what you mean. What kind of wrapper do > you mean? What does it wrap, and what does it set? The problem with the > multiple outputs is that when you would add each to PYTHONPATH, the extra > outputs won't be importable unless the 'main' output is first. I don't see > how that can be solved. One that sets PYTHONPATH? Or some kind of package > I had in mind a simple ```combine [blah.foo blah.bar]``` that would > produce a derivation with symlinks to both $foo/lib/python2.7/blah/foo and > $foo/lib/python2.7/blah/bar, so multiple outputs are combined back and can > be importable with the current envHook setting the PYTHONPATH. This is > similar to the current python wrapper that additionally throws in the > python interpreter itself along with wrapper to set PYTHONHOME. > > > > > As for the first point, I couldn’t very well understand what the > problem is. Are you talking about conflict between instances of a package > that were built against different version of the python? Then shouldn’t > `--prefix` override the incompatible version, since, as you said, order > matters? > > > > Example with discussion: https://github.com/NixOS/nixpkgs/pull/17749 > > > > > > On Tue, Nov 1, 2016 at 4:12 PM, Dmitry Kalinkin < > [email protected]> wrote: > > > > > On 01 Nov 2016, at 06:22, Freddy Rietdijk <[email protected]> > wrote: > > > > > > Hi, > > > > > > Currently we use PYTHONPATH a lot in Nixpkgs to let applications and > the interpreter find Python modules. This typically works fine, but there > are problems with this method and so I would like to get rid of it and use > only `python.withPackages` which uses `python.buildEnv`. > > > > > > The two main issues with the use of PYTHONPATH: > > > • Before we used `--prefix $PYTHONPATH`, but this would leak > PYTHONPATH into subprocesses, which is especially problematic when both > parent and child depend on Python but of different versions. `--set > $PYTHONPATH` would solve that issue, but that makes it impossible to add > other (impure) paths, which is an important feature. This also breaks > alternative shells like `ipython`. This issue is currently solved by > extending `sys.path` in the Python applications. > > > • Limits the use of multiple outputs. When moving a module of a > package into a separate output it becomes problematic to load this again, > since just adding the module to PYTHONPATH typically doesn't work because > the order matters. While Python modules are typically small, and build > fast, rebuilding can take a lot of time in cases like `matplotlib` which > supports multiple backends and is depended on by quite some packages. > > > A method that is more reliable is building an environment with > symbolic links to all the modules, and wrapping the applications with a > wrapper that sets PYTHONHOME. This is exactly what `python.buildEnv` does, > and it solves both 1) and 2). > > > > > > `PYTHONPATH` is mainly constructed with the Python interpreter > setupHook. It is used in `buildPythonPackage` for building the package, and > after installing it is extended so the tests can run. Furthermore, > `PYTHONPATH` is set by the `setupHook` when using `nix-shell` like > `nix-shell -p pythonPackages.numpy`. > > > > > > I think we can get rid of the setupHook. For the building we can > create an env. This would be able to support multiple outputs as inputs, > but will be more expensive than setting PYTHONPATH. For the tests we do add > the newly constructed package to PYTHONPATH; there's no way around it and > it doesn't cause any problems either. > > > > > > The biggest impact will be on how `nix-shell` is used. It won't be > possible anymore to use it as shown before, instead `nix-shell -p > 'python.withPackages(ps:[ps.numpy])'` would have to be used. While it is > possible to keep the setupHook (or use it as a shellHook) it will be > unreliable in the case of multiple outputs. > > > > > > What do you think about this change? Do you see any problems with it? > Any other suggestions? > > > > > > Freddy > > > _______________________________________________ > > > nix-dev mailing list > > > [email protected] > > > http://lists.science.uu.nl/mailman/listinfo/nix-dev > > > > Hi, > > > > I’m far from being an expert in python, but here are my thoughts: > > > > To solve 2) you could also make a wrapper that combines selected outputs > of the multiple output package without python itself. I think, this is what > texlive does. That way all the burden of wrapping will be limited only to > the multiple output packages. As for the first point, I couldn’t very well > understand what the problem is. Are you talking about conflict between > instances of a package that were built against different version of the > python? Then shouldn’t `--prefix` override the incompatible version, since, > as you said, order matters? > > > > Also, if you remove setupHook, won’t you also lose ability to specify > python dependencies directly in buildInputs? Put that inside mkDerivation? > > > > Dmitry > > > > _______________________________________________ > nix-dev mailing list > [email protected] > http://lists.science.uu.nl/mailman/listinfo/nix-dev >
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