python{2,3}.pkgs.gobject3 with GTK3 - not found?

[ashgillman]

Issue description

Matplotlib with the GTK3 backend doesn't seem to be working. However, I am not actually sure how this feature is intended to be used.

Steps to reproduce

# matplotlib.nix
with import <nixpkgs> {};
# (python3.withPackages (pkgs: with pkgs; [ (matplotlib.override { enableGtk3 = true; }) ])).env
(python2.withPackages (pkgs: with pkgs; [ (matplotlib.override { enableGtk3 = true; }) ])).env

$ nix-shell matplotlib.nix
[nix-shell:~/tmp]$ MPLBACKEND=GTK3Cairo python
Python 2.7.14 (default, Sep 16 2017, 17:49:51)
[GCC 6.4.0] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> from matplotlib import pyplot as plt
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/nix/store/v90d6zrgljzvjvibm97ssm9pm0ha8bin-python-2.7.14-env/lib/python2.7/site-packages/matplotlib/pyplot.py", line 115, in <module>
    _backend_mod, new_figure_manager, draw_if_interactive, _show = pylab_setup()
  File "/nix/store/v90d6zrgljzvjvibm97ssm9pm0ha8bin-python-2.7.14-env/lib/python2.7/site-packages/matplotlib/backends/__init__.py", line 32, in pylab_setup
    globals(),locals(),[backend_name],0)
  File "/nix/store/v90d6zrgljzvjvibm97ssm9pm0ha8bin-python-2.7.14-env/lib/python2.7/site-packages/matplotlib/backends/backend_gtk3cairo.py", line 6, in <module>
    from . import backend_gtk3
  File "/nix/store/v90d6zrgljzvjvibm97ssm9pm0ha8bin-python-2.7.14-env/lib/python2.7/site-packages/matplotlib/backends/backend_gtk3.py", line 21, in <module>
    "Gtk3 backend requires the GObject introspection bindings for Gtk 3 "
ImportError: Gtk3 backend requires the GObject introspection bindings for Gtk 3 to be installed.
>>>

Technical details

Please run nix-shell -p nix-info --run "nix-info -m" and paste the
results.

• system: "x86_64-linux"
• host os: Linux 4.13.0-38-generic, Ubuntu, 16.04.4 LTS (Xenial Xerus)
• multi-user?: no
• sandbox: no
• version: nix-env (Nix) 2.0
• channels(gil2a4): "nixpkgs-18.03pre126020.931a0b8be80"
• channels(root): ""
• nixpkgs: /etc/nixpkgs

^ have also run on the latest 18.03

[ashgillman]

Actually,

$ nix-shell -p 'python3.pkgs.matplotlib.override { enableGtk3 = true; }'

Seems to work. Why doesn't my first method?

[jtojnar]

Duplicate of #39637?

GObject bindings require some environments variables to be set (at least GI_TYPELIB_PATH). In normal case, gobjectIntrospecion’s setup hook would populate it, and then wrapGAppsHook would wrap the executable files. With python libraries, there is no executable to be wrapped, but in some cases the variables might get into the shell. I am not exactly sure about nix-shell semantics, but something like the following might work:

# matplotlib.nix
with import <nixpkgs> {};

let
  matplotlib = python3.pkgs.matplotlib.override { enableGtk3 = true; };
in stdenv.mkDerivation rec {
  name = "my-statistics-tools";

  buildInputs = [
    python
    matplotlib # probably needs to be separate for environment variables to propagate correctly
  ];

  shellHook = ''
    MPLBACKEND=GTK3Cairo exec python
  '';
}

It segfaults for me, though.

[ashgillman]

@jtojnar You tagged this issue as the duplicate by accident :)

[jtojnar]

Right, I meant #25351

[balsoft]

@jtojnar I have a similar issue of python segfaulting when I try to import Gtk from gi.repository.
My script:

#!/usr/bin/env nix-shell
#!nix-shell -p python36Packages.pygobject3 -p gobjectIntrospection -p gtk3 -i python3

import gi
gi.require_version("Gtk", "3.0")
from gi.repository import Gtk

Results in Segmentation fault every time.

[stale]

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[nixos-discourse]

This issue has been mentioned on NixOS Discourse. There might be relevant details there:

https://discourse.nixos.org/t/python-matplotlib-gtk-backend-not-working/17419/5