GNU bug report logs - #70687
python-matplotlib not respecting env var MPLBACKEND=TkAgg

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Jake <jforst.mailman <at> gmail.com>
To: bug-guix <at> gnu.org
Subject: python-matplotlib not respecting env var MPLBACKEND=TkAgg
Date: Wed, 1 May 2024 01:23:19 +0000

[Message part 1 (text/plain, inline)]

Hello

We are supposed to be able to control the backend used by Python's
Matplotlib via the MPLBACKEND environment variable [1]. This doesn't appear
to work for the TkAgg backend:

#+begin_src sh

  guix shell python python-matplotlib -- bash -c 'MPLBACKEND=TkAgg python3
-c "import matplotlib; print(matplotlib.get_backend()); import
matplotlib.pyplot as plt; plt.plot([1],[2]); plt.show()"'

#+end_src

#+RESULTS:
: TkAgg
: <string>:1: UserWarning: FigureCanvasAgg is non-interactive, and thus
cannot be shown

However, the TkAgg backend does work if it is hardcoded in the Python
script using `matplotlib.use()`:

#+begin_src sh

  guix shell python python-matplotlib -- python3 -c "import matplotlib;
matplotlib.use('TkAgg'); print(matplotlib.get_backend()); import
matplotlib.pyplot as plt; plt.plot([1],[2]); plt.show()"

#+end_src

#+RESULTS:
: TkAgg

Thanks
Jake

[1]: https://matplotlib.org/stable/users/explain/figure/backends.html

[Message part 2 (text/html, inline)]

Message #8 received at 70687 <at> debbugs.gnu.org (full text, mbox):

From: Jake <jforst.mailman <at> gmail.com>
To: 70687 <at> debbugs.gnu.org
Cc: me <at> bonfacemunyoki.com, sharlatanus <at> gmail.com, tanguy <at> bioneland.org,
 lars <at> 6xq.net
Subject: Re: bug#70687: python-matplotlib not respecting env var
 MPLBACKEND=TkAgg
Date: Thu, 3 Apr 2025 11:36:49 +0000

[Message part 1 (text/plain, inline)]

It appears that importing matplotlib.pyplot resets the Matplotlib backend
to Agg.

  $ guix shell python python-matplotlib -- bash -c 'MPLBACKEND=tkagg
python3 -c "import matplotlib; print(matplotlib.get_backend()); import
matplotlib.pyplot; print(matplotlib.get_backend())"'

  TkAgg
  agg


On Wed, May 1, 2024 at 1:25 AM Jake <jforst.mailman <at> gmail.com> wrote:

> Hello
>
> We are supposed to be able to control the backend used by Python's
> Matplotlib via the MPLBACKEND environment variable [1]. This doesn't appear
> to work for the TkAgg backend:
>
> #+begin_src sh
>
>   guix shell python python-matplotlib -- bash -c 'MPLBACKEND=TkAgg python3
> -c "import matplotlib; print(matplotlib.get_backend()); import
> matplotlib.pyplot as plt; plt.plot([1],[2]); plt.show()"'
>
> #+end_src
>
> #+RESULTS:
> : TkAgg
> : <string>:1: UserWarning: FigureCanvasAgg is non-interactive, and thus
> cannot be shown
>
> However, the TkAgg backend does work if it is hardcoded in the Python
> script using `matplotlib.use()`:
>
> #+begin_src sh
>
>   guix shell python python-matplotlib -- python3 -c "import matplotlib;
> matplotlib.use('TkAgg'); print(matplotlib.get_backend()); import
> matplotlib.pyplot as plt; plt.plot([1],[2]); plt.show()"
>
> #+end_src
>
> #+RESULTS:
> : TkAgg
>
> Thanks
> Jake
>
> [1]: https://matplotlib.org/stable/users/explain/figure/backends.html
>

[Message part 2 (text/html, inline)]

Message #11 received at 70687 <at> debbugs.gnu.org (full text, mbox):

From: Liliana Marie Prikler <liliana.prikler <at> gmail.com>
To: Jake <jforst.mailman <at> gmail.com>, 70687 <at> debbugs.gnu.org
Cc: me <at> bonfacemunyoki.com, tanguy <at> bioneland.org, sharlatanus <at> gmail.com,
 lars <at> 6xq.net
Subject: Re: bug#70687: python-matplotlib not respecting env var
 MPLBACKEND=TkAgg
Date: Sun, 06 Apr 2025 01:00:44 +0200

Hi Jake,

Am Donnerstag, dem 03.04.2025 um 11:36 +0000 schrieb Jake:
> It appears that importing matplotlib.pyplot resets the Matplotlib
> backend to Agg.
> 
>   $ guix shell python python-matplotlib -- bash -c 'MPLBACKEND=tkagg
> python3 -c "import matplotlib; print(matplotlib.get_backend());
> import matplotlib.pyplot; print(matplotlib.get_backend())"'
> 
>   TkAgg
>   agg
I recently encountered the same issue.  The issue is that matplotlib
internally sources a configuration file that sets the backend *after*
reading the environment variable.  To circumvent this, you use
something along the lines of the following code until the issue is
fixed:

  from matplotlib import set_backend 
  from os import environ
  
  […]

  if __name__ == '__main__':
    if 'MPLBACKEND' in environ: set_backend(environ['MPLBACKEND'])
    […]

Cheers

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