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I am trying to use pythonix to import some local files and run some unit tests. However, it doesn't seem to parse relative paths properly. All of these methods work in the Nix REPL.

>>>import nix

>>> nix.eval('with import ./math.nix; isEven 2')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
nix.NixError: not an absolute path: '././math.nix'

>>> nix.eval('with import (./. + "math.nix"); isEven 2')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
nix.NixError: not an absolute path: '././.'

>>> nix.eval('with import (builtins.toString ./math.nix); isEven 2')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
nix.NixError: not an absolute path: '././math.nix'

Is it possible with pythonix to view a derivation similar to "nix show-derivation ..."? I have tried nix.eval("with import {}; python3Packages.numpy") and ran into errors. Maybe this is not the correct way to view a derivation output? My end goal is that I want to create an adjacency matrix of runtime vs test vs build time python dependencies. But I have plans to use all the derivations to gather statistics. Right now the big limitation for me is how to extract this from nix.

Currently in Nixpkgs python3 is python38, and python3Packages.pythonix is built correctly, but python37Packages.pythonix and python39Packages.pythonix both install nix.so in lib/python3.8/site-packages, thus a dependent package python39Packages.nixpkgs fails to import nix: NixOS/nixpkgs#107623 (comment)

I don't know whether the root cause of this issue is in pythonix (in how it uses meson), meson (which seems most likely to me), or Nixpkgs.

I wanted to open an issue to judge what you think about exposing the nix expression AST in pythonix. This package is already great for evaluating expressions and working with the results in python. I would like to add a PR for AST support because this would enable a whole set of tooling to be easily made. For example

• automate alphabetically sorting packages
• automate enforcing a code style to expressions
• could also benefit code editors with handling nix expressions

I have already found that the AST is exposed at https://github.com/NixOS/nix/blob/master/src/libexpr/nixexpr.hh . I will need to have knowledge of interfacing C++ with python for my future job (without using cython) and I think this is a doable project that could provide a lot of benefit.

Steps to reproduce:

nix-shell -p 'python3.withPackages(ps: with ps; [ python3Packages.pythonix ])'

Error:

../src/python-to-nix.cc: In function ‘nix::Value* pythonnix::pythonToNixValue(nix::EvalState&, PyObject*)’:
../src/python-to-nix.cc:85:41: error: invalid conversion from ‘const char*’ to ‘char*’ [-fpermissive]
     char *utf8 = PyUnicode_AsUTF8AndSize(obj, &size);
                  ~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~

Or is that a packaging issue?