pyplot not working in ipython

[btlvr]

I'm using NixOS 19.09, and I'm unable to use pyplot from within ipython. It works in a normal Python interpreter.

λ python3.7
Python 3.7.5 (default, Oct 14 2019, 23:08:55) 
[GCC 8.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import matplotlib.pyplot as plt
>>> quit()
λ 

λ ipython3
Python 3.7.5 (default, Oct 14 2019, 23:08:55) 
Type 'copyright', 'credits' or 'license' for more information
IPython 7.6.1 -- An enhanced Interactive Python. Type '?' for help.

In [1]: import matplotlib.pyplot as plt                                                                                                                                                                 

In [2]: qt.qpa.plugin: Could not find the Qt platform plugin "xcb" in ""                                                                                                                                
This application failed to start because no Qt platform plugin could be initialized. Reinstalling the application may fix this problem.

zsh: abort (core dumped)  ipython3
λ    

[FRidh]

How did you bring python and ipython in your environment?

[rnhmjoj]

Strangely enough, I'm getting the exact same problem in standard CPython interpreter, so it's probably not an issue in ipython.

How did you bring python and ipython in your environment?

let
    python' = python3.override {
      packageOverrides = self: super: {
        matplotlib = super.matplotlib.override { enableQt = true; };
      };
    };
in python'.withPackages (p: [ p.matplotlib ]);

Here I'm on nixos 20.03 (ceb90b0).

[rnhmjoj]

I'm linking the issue related to this: #25351 #53816.
I guess something recently changed because the Qt backend used to work: I'll try bisecting.

[wucke13]

Just a small heads-up: use the matplotlib TK backend in the meantime, it is sleek and works.

[FRidh]

I think matplotlib should propagate the wrap Qt hook when Qt is included in matplotlib. In Python's buildEnv we should then include qtWrapperArgs[@].

[rnhmjoj]

@FRidh: I like the idea. To be sure, do you mean the python.withPackages defined here? I could try to implement it: it doesn't seem too difficult.

[stale]

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[rnhmjoj]

It's still an open problem.

[bhipple]

Is there a recommended workaround for QT support in matplotlib?

[rnhmjoj]

I had a working proposal that could have made it into 20.09, but it has been scrapped in favour of more complex solution (#102949), which seems stalled :(.

If you really need this to work, try creating a shell.nix in which you define the variables set by makeWrapper. We are lucky matplotlib backend doesn't require any qml/qt plugin except the base, so this should be enough:

let
  pkgs = import <nixpkgs> { };

  matplotlib = pkgs.python3Packages.matplotlib.override { enableQt = true; };

in
  pkgs.mkShell {
    buildInputs = [ matplotlib ];

    QT_PLUGIN_PATH = with pkgs.qt5; "${qtbase}/${qtbase.qtPluginPrefix}";

    shellHook = "python -i";
  }

[stale]

I marked this as stale due to inactivity. → More info

[rnhmjoj]

Still an issue

[jamesdbrock]

See also #236770