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

Message #14 received at 70687 <at> debbugs.gnu.org (full text, mbox):

From: Jake <jforst.mailman <at> gmail.com>
To: Liliana Marie Prikler <liliana.prikler <at> gmail.com>
Cc: me <at> bonfacemunyoki.com, 70687 <at> debbugs.gnu.org, 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: Thu, 3 Jul 2025 13:19:54 +0000

Hi Lily

It looks like this bug isn't going away anytime soon.

Here is the offending code in `lib/matplotlib/pyplot.py`, with an
added print statement:

```text
# If rcParams['backend_fallback'] is true, and an interactive backend is
# requested, ignore rcParams['backend'] and force selection of a backend that
# is compatible with the current running interactive framework.
if (rcParams["backend_fallback"]
        and rcParams._get_backend_or_none() in (  # type: ignore
            set(rcsetup.interactive_bk) - {'WebAgg', 'nbAgg'})
        and cbook._get_running_interactive_framework()):  # type: ignore
    print(f"running interactive framework is:
{cbook._get_running_interactive_framework()}")
    rcParams._set("backend", rcsetup._auto_backend_sentinel)  # type: ignore
```

Running this

```text
MPLBACKEND=tkagg guix shell
--with-source=python-matplotlib=$HOME/matplotlib
--without-tests=python-matplotlib python python-matplotlib -- python3
-c "import matplotlib; print(matplotlib.get_backend()); import
matplotlib.pyplot as plt; print(matplotlib.get_backend())"
```

gives

```text
TkAgg
running interactive framework is: headless
agg
```

So I guess the next question is: why does it think I'm headless?  To
be continued...

Thanks
Jake


On Sat, Apr 5, 2025 at 11:00 PM Liliana Marie Prikler
<liliana.prikler <at> gmail.com> wrote:
>
> 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

Message #17 received at 70687 <at> debbugs.gnu.org (full text, mbox):

From: Jake <jforst.mailman <at> gmail.com>
To: Liliana Marie Prikler <liliana.prikler <at> gmail.com>
Cc: me <at> bonfacemunyoki.com, 70687 <at> debbugs.gnu.org, 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: Thu, 3 Jul 2025 13:48:25 +0000

Continuing:
In `lib/matplotlib/cbook.py`, the function
`_get_running_interactive_framework` has:

```text
    if not _c_internal_utils.display_is_valid():
        return "headless"
```

In `src/_c_internal_utils.c` we have this docstring for `display_is_valid`:

```text
     "Check whether the current X11 or Wayland display is valid.\n\n"
     "On Linux, returns True if either $DISPLAY is set and XOpenDisplay(NULL)\n"
     "succeeds, or $WAYLAND_DISPLAY is set and wl_display_connect(NULL)\n"
     "succeeds.\n\n"
     "On other platforms, always returns True."},
```

$DISPLAY is set, so it must be XOpenDisplay(NULL) failing...

I found a post [1] from a Nix user:
> For anyone else facing similar issues - I resolved this by adding the X11 library to the LD_LIBRARY_PATH of my development shell.

But I haven't made any more progress.

Cheers
Jake

[1] https://discourse.nixos.org/t/python-matplotlib-tkinter-matplotlib-reverts-to-agg-backend-because-it-cant-find-a-valid-display/45064

On Thu, Jul 3, 2025 at 1:19 PM Jake <jforst.mailman <at> gmail.com> wrote:
>
> Hi Lily
>
> It looks like this bug isn't going away anytime soon.
>
> Here is the offending code in `lib/matplotlib/pyplot.py`, with an
> added print statement:
>
> ```text
> # If rcParams['backend_fallback'] is true, and an interactive backend is
> # requested, ignore rcParams['backend'] and force selection of a backend that
> # is compatible with the current running interactive framework.
> if (rcParams["backend_fallback"]
>         and rcParams._get_backend_or_none() in (  # type: ignore
>             set(rcsetup.interactive_bk) - {'WebAgg', 'nbAgg'})
>         and cbook._get_running_interactive_framework()):  # type: ignore
>     print(f"running interactive framework is:
> {cbook._get_running_interactive_framework()}")
>     rcParams._set("backend", rcsetup._auto_backend_sentinel)  # type: ignore
> ```
>
> Running this
>
> ```text
> MPLBACKEND=tkagg guix shell
> --with-source=python-matplotlib=$HOME/matplotlib
> --without-tests=python-matplotlib python python-matplotlib -- python3
> -c "import matplotlib; print(matplotlib.get_backend()); import
> matplotlib.pyplot as plt; print(matplotlib.get_backend())"
> ```
>
> gives
>
> ```text
> TkAgg
> running interactive framework is: headless
> agg
> ```
>
> So I guess the next question is: why does it think I'm headless?  To
> be continued...
>
> Thanks
> Jake
>
>
> On Sat, Apr 5, 2025 at 11:00 PM Liliana Marie Prikler
> <liliana.prikler <at> gmail.com> wrote:
> >
> > 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

Message #20 received at 70687 <at> debbugs.gnu.org (full text, mbox):

From: Jake <jforst.mailman <at> gmail.com>
To: Liliana Marie Prikler <liliana.prikler <at> gmail.com>
Cc: me <at> bonfacemunyoki.com, 70687 <at> debbugs.gnu.org, 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: Fri, 4 Jul 2025 17:39:13 +0930

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

Fixed, I think.  We just need to patch a dlopen call.

Now TkAgg works out of the box, without requiring changes to user Python
code.  I hope that also means we can change the default backend from Agg to
TkAgg.

Submitted this PR (and got lucky number 1000!)
https://codeberg.org/guix/guix/pulls/1000
with the fix and change of backend.

Cheers
Jake

On Thu, 3 Jul 2025 at 11:18 pm, Jake <jforst.mailman <at> gmail.com> wrote:

> Continuing:
> In `lib/matplotlib/cbook.py`, the function
> `_get_running_interactive_framework` has:
>
> ```text
>     if not _c_internal_utils.display_is_valid():
>         return "headless"
> ```
>
> In `src/_c_internal_utils.c` we have this docstring for `display_is_valid`:
>
> ```text
>      "Check whether the current X11 or Wayland display is valid.\n\n"
>      "On Linux, returns True if either $DISPLAY is set and
> XOpenDisplay(NULL)\n"
>      "succeeds, or $WAYLAND_DISPLAY is set and wl_display_connect(NULL)\n"
>      "succeeds.\n\n"
>      "On other platforms, always returns True."},
> ```
>
> $DISPLAY is set, so it must be XOpenDisplay(NULL) failing...
>
> I found a post [1] from a Nix user:
> > For anyone else facing similar issues - I resolved this by adding the
> X11 library to the LD_LIBRARY_PATH of my development shell.
>
> But I haven't made any more progress.
>
> Cheers
> Jake
>
> [1]
> https://discourse.nixos.org/t/python-matplotlib-tkinter-matplotlib-reverts-to-agg-backend-because-it-cant-find-a-valid-display/45064
>
> On Thu, Jul 3, 2025 at 1:19 PM Jake <jforst.mailman <at> gmail.com> wrote:
> >
> > Hi Lily
> >
> > It looks like this bug isn't going away anytime soon.
> >
> > Here is the offending code in `lib/matplotlib/pyplot.py`, with an
> > added print statement:
> >
> > ```text
> > # If rcParams['backend_fallback'] is true, and an interactive backend is
> > # requested, ignore rcParams['backend'] and force selection of a backend
> that
> > # is compatible with the current running interactive framework.
> > if (rcParams["backend_fallback"]
> >         and rcParams._get_backend_or_none() in (  # type: ignore
> >             set(rcsetup.interactive_bk) - {'WebAgg', 'nbAgg'})
> >         and cbook._get_running_interactive_framework()):  # type: ignore
> >     print(f"running interactive framework is:
> > {cbook._get_running_interactive_framework()}")
> >     rcParams._set("backend", rcsetup._auto_backend_sentinel)  # type:
> ignore
> > ```
> >
> > Running this
> >
> > ```text
> > MPLBACKEND=tkagg guix shell
> > --with-source=python-matplotlib=$HOME/matplotlib
> > --without-tests=python-matplotlib python python-matplotlib -- python3
> > -c "import matplotlib; print(matplotlib.get_backend()); import
> > matplotlib.pyplot as plt; print(matplotlib.get_backend())"
> > ```
> >
> > gives
> >
> > ```text
> > TkAgg
> > running interactive framework is: headless
> > agg
> > ```
> >
> > So I guess the next question is: why does it think I'm headless?  To
> > be continued...
> >
> > Thanks
> > Jake
> >
> >
> > On Sat, Apr 5, 2025 at 11:00 PM Liliana Marie Prikler
> > <liliana.prikler <at> gmail.com> wrote:
> > >
> > > 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
>

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

Message #25 received at 70687-done <at> debbugs.gnu.org (full text, mbox):

From: Simon Tournier <zimon.toutoune <at> gmail.com>
To: Jake <jforst.mailman <at> gmail.com>, Liliana Marie Prikler
 <liliana.prikler <at> gmail.com>
Cc: me <at> bonfacemunyoki.com, sharlatanus <at> gmail.com, 70687-done <at> debbugs.gnu.org,
 tanguy <at> bioneland.org, lars <at> 6xq.net
Subject: Re: bug#70687: python-matplotlib not respecting env var
 MPLBACKEND=TkAgg
Date: Wed, 20 Aug 2025 17:47:32 +0200

Hi,

On Fri, 04 Jul 2025 at 17:39, Jake <jforst.mailman <at> gmail.com> wrote:
> Fixed, I think.  We just need to patch a dlopen call.
>
> Now TkAgg works out of the box, without requiring changes to user Python
> code.  I hope that also means we can change the default backend from Agg to
> TkAgg.
>
> Submitted this PR (and got lucky number 1000!)
> https://codeberg.org/guix/guix/pulls/1000
> with the fix and change of backend.

As far as I see, guix/guix#1000 had been merged, so I’m closing this
issue.

If I’m missing something, feel free to reopen. :-)

Cheers,
simon

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