bug#70687: python-matplotlib not respecting env var MPLBACKEND=TkAgg

[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

On Wed, May 1, 2024 at 1:25 AM Jake <jforst.mailman@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