Python matplotlib Gtk backend not working

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1

Hello community,

I am trying to set up my Python scientific environment in NixOS 21.11, and I have stumbled against some issues with the matplotlib library. More specifically, I get the following error when trying to use the Gtk backend:

$ python -c 'import matplotlib.pyplot as plt; plt.plot()'
Traceback (most recent call last):
  File "/nix/store/mar5qp8knkprymbany0h1ildlz5lf7i3-python3-3.9.6-env/lib/python3.9/site-packages/matplotlib/backends/backend_gtk3.py", line 24, in <module>
    gi.require_version("Gtk", "3.0")
  File "/nix/store/mar5qp8knkprymbany0h1ildlz5lf7i3-python3-3.9.6-env/lib/python3.9/site-packages/gi/__init__.py", line 126, in require_version
    raise ValueError('Namespace %s not available' % namespace)
ValueError: Namespace Gtk not available

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "/nix/store/mar5qp8knkprymbany0h1ildlz5lf7i3-python3-3.9.6-env/lib/python3.9/site-packages/matplotlib/pyplot.py", line 2500, in <module>
    switch_backend(rcParams["backend"])
  File "/nix/store/mar5qp8knkprymbany0h1ildlz5lf7i3-python3-3.9.6-env/lib/python3.9/site-packages/matplotlib/pyplot.py", line 277, in switch_backend
    class backend_mod(matplotlib.backend_bases._Backend):
  File "/nix/store/mar5qp8knkprymbany0h1ildlz5lf7i3-python3-3.9.6-env/lib/python3.9/site-packages/matplotlib/pyplot.py", line 278, in backend_mod
    locals().update(vars(importlib.import_module(backend_name)))
  File "/nix/store/19j43hyh37jqnn9l7rg6shk5barbn209-python3-3.9.6/lib/python3.9/importlib/__init__.py", line 127, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "/nix/store/mar5qp8knkprymbany0h1ildlz5lf7i3-python3-3.9.6-env/lib/python3.9/site-packages/matplotlib/backends/backend_gtk3agg.py", line 8, in <module>
    from . import backend_agg, backend_gtk3
  File "/nix/store/mar5qp8knkprymbany0h1ildlz5lf7i3-python3-3.9.6-env/lib/python3.9/site-packages/matplotlib/backends/backend_gtk3.py", line 28, in <module>
    raise ImportError from e
ImportError

This is my current python config in environment.systemPackages:

    (let
      my-python-packages = python-packages: with python-packages; [
        # Scientific libraries
        pandas
        numpy
        scipy
        matplotlib
        jupyter
        ipython
        # Gtk hell
        pygobject3
        pycairo
      ];
      python-with-my-packages = python3.withPackages my-python-packages;
    in
      python-with-my-packages)

I have also in installed the packages gtk3, cairo, and gobject-introspection, but I still get the same error. Any hint on how to solve this issue? Thanks in advance.

2

Hi!

I tried around for half an hour now, and give up. I thought, hey this is an easy one, but nope. To be honest, I think this is bugged, but let’s wait for other opinions. What I got:

  packageOverrides = self: super: {
    matplotlib = super.matplotlib.override { enableGtk3 = true; };
  };
  myPython = pkgs.python3.override { inherit packageOverrides; };
  myPythonPackages = ppkgs: with ppkgs; [
    ipython
    matplotlib
  ];
  myPythonEnvironment = myPython.withPackages myPythonPackages;

This works somewhat. It definitely sets the flag, and rebuilds a lot of things when adding other Python packages (sucks). However, I get the same error as you do. So it seems that there is a deeper problem.

For reference, the Python code to get the error message:

import matplotlib
import matplotlib.pyplot as plt
matplotlib.use("GTK3Cairo")

EDIT: Maybe it is worth trying a system-wide overlay. I didn’t use a system-wide overlay here.

3

Anybody? Should we move this to the Git repo issue list?

4

AFAIK, there’s nothing against it in this case. Just go ahead and file an issue.

The current maintainers of python3Packages.matplotlib are lovek323 and veprbl. There will be a section inside the issue template for you to ping them.

5

This is a well known issue, you need GI_TYPELIB_PATH set. We have an infrastructure for that but it relies on wrappers so it can only be done on a leaf package that is a program.

If you search, you should see several issues and discourse threads talking about this (e.g python{2,3}.pkgs.gobject3 with GTK3 - not found? · Issue #39637 · NixOS/nixpkgs · GitHub).