Camelot fails because of missing ghostscript dependency

[matthuszagh]

Take the following flake (nixpkgs rev is 1e56a3b):

{
  inputs.nixpkgs.url = github:nixos/nixpkgs;

  outputs =
    { self
    , nixpkgs
    }: {
      devShell.x86_64-linux =
        let
          system = "x86_64-linux";
          pkgs = (import nixpkgs { inherit system; }).pkgs;
        in
        pkgs.mkShell {
          buildInputs = (with pkgs; [
            (python3.withPackages (p: with p; [
              camelot
            ]))
          ]);
        };
    };
}

Now, start python and (or presumably use any other PDF)

import camelot
tables = camelot.read_pdf("tlv3511-q1.pdf")

This emits the error:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/nix/store/8kbmmpb8r84y89132q6bpcj85an1n0sv-python3-3.12.7-env/lib/python3.12/site-packages/camelot/io.py", line 113, in read_pdf
    tables = p.parse(
             ^^^^^^^^
  File "/nix/store/8kbmmpb8r84y89132q6bpcj85an1n0sv-python3-3.12.7-env/lib/python3.12/site-packages/camelot/handlers.py", line 176, in parse
    t = parser.extract_tables(
        ^^^^^^^^^^^^^^^^^^^^^^
  File "/nix/store/8kbmmpb8r84y89132q6bpcj85an1n0sv-python3-3.12.7-env/lib/python3.12/site-packages/camelot/parsers/lattice.py", line 421, in extract_tables
    self.backend.convert(self.filename, self.imagename)
  File "/nix/store/8kbmmpb8r84y89132q6bpcj85an1n0sv-python3-3.12.7-env/lib/python3.12/site-packages/camelot/backends/ghostscript_backend.py", line 31, in convert
    raise OSError(
OSError: Ghostscript is not installed. You can install it using the instructions here: https://camelot-py.readthedocs.io/en/master/user/install-deps.html

I can explicitly provide ghostscript in the flake with (though it should be a runtime dependency)

{
  inputs.nixpkgs.url = github:nixos/nixpkgs;

  outputs =
    { self
    , nixpkgs
    }: {
      devShell.x86_64-linux =
        let
          system = "x86_64-linux";
          pkgs = (import nixpkgs { inherit system; }).pkgs;
        in
        pkgs.mkShell {
          buildInputs = (with pkgs; [
            (python3.withPackages (p: with p; [
              camelot
            ]))
            ghostscript
          ]);
        };
    };
}

Then, the error is

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/nix/store/8kbmmpb8r84y89132q6bpcj85an1n0sv-python3-3.12.7-env/lib/python3.12/site-packages/camelot/io.py", line 113, in read_pdf
    tables = p.parse(
             ^^^^^^^^
  File "/nix/store/8kbmmpb8r84y89132q6bpcj85an1n0sv-python3-3.12.7-env/lib/python3.12/site-packages/camelot/handlers.py", line 176, in parse
    t = parser.extract_tables(
        ^^^^^^^^^^^^^^^^^^^^^^
  File "/nix/store/8kbmmpb8r84y89132q6bpcj85an1n0sv-python3-3.12.7-env/lib/python3.12/site-packages/camelot/parsers/lattice.py", line 421, in extract_tables
    self.backend.convert(self.filename, self.imagename)
  File "/nix/store/8kbmmpb8r84y89132q6bpcj85an1n0sv-python3-3.12.7-env/lib/python3.12/site-packages/camelot/backends/ghostscript_backend.py", line 36, in convert
    import ghostscript
ModuleNotFoundError: No module named 'ghostscript'

@2gn @bcdarwin

[2gn]

We might need to package the ghostscript Python package to successfully build the package—apologies for the inconvenience. In the meantime, you could consider using a tool like devenv to run your program.

[matthuszagh]

Thanks for the suggestion. I'm not too familiar with devenv but (among other things) it sounds like it makes it easy to use packages from various versions of nixpkgs. Is that right? In that case, are you suggesting I take an old version of camelot, or that the ghostscript python package was previously available in nixpkgs?

I tried pinning nixpkgs to rev b6dbd73 (the commit in which camelot was introduced), but I still get the same "No module named 'ghostscript'" error in that case.

[2gn]

it sounds like it makes it easy to use packages from various versions of nixpkgs.

Maybe, but I used it for managing my python projects. See: https://devenv.sh/supported-languages/python/#languagespythondirectory

specifying camelot somewhere like languages.python.uv.package should work because this way the package installation doesn't depend on Nix, but will still be managed by Nix ecosystem.

[amarshall]

Should be fixed by #391671, please test and review if possible.