matplotlib is not available, graph is not shown

[Celal ERGÜN]

Hi all. I've been using Pondus for a long time. After upgrading to 18.04 graph stopped working and the graph button is greyed out. If I hover on the button a hint appears, saying "matplotlib not available". I tried to install matplotlib by "apt install" or pip but definitely I am not a Python guy.

Then I tried to start the program from CLI (Kubuntu Konsole and standart Ubuntu terminal). I got the following message at start up:

Exception in thread Thread-1:
Traceback (most recent call last):
  File "/usr/lib/python2.7/threading.py", line 801, in __bootstrap_inner
    self.run()
  File "/usr/lib/python2.7/dist-packages/pondus/gui/window_main.py", line 359, in run
    import_mpl()
  File "/usr/lib/python2.7/dist-packages/pondus/gui/window_main.py", line 374, in import_mpl
    from pondus.gui.dialog_plot import PlotDialog
  File "/usr/lib/python2.7/dist-packages/pondus/gui/dialog_plot.py", line 17, in <module>
    from matplotlib.backends.backend_gtkagg import FigureCanvasGTKAgg \
  File "/usr/lib/python2.7/dist-packages/matplotlib/backends/backend_gtkagg.py", line 14, in <module>
    from matplotlib.backends.backend_gtk import (
  File "/usr/lib/python2.7/dist-packages/matplotlib/backends/backend_gtk.py", line 35, in <module>
    from matplotlib.backends.backend_gdk import RendererGDK, FigureCanvasGDK
  File "/usr/lib/python2.7/dist-packages/matplotlib/backends/backend_gdk.py", line 33, in <module>
    from matplotlib.backends._backend_gdk import pixbuf_get_pixels_array
ImportError: No module named _backend_gdk

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[PauricTheLodger (ptl)]

I've been experiencing the same error. It looks to have already been reported at matplotlib (https://github.com/matplotlib/matplotlib/issues/8441/) and sounds like python-matplotlib was built from a wheel rather than source with the gdk2 header files?

[tomasso (john-expat-world)]

I can confirm, too. However, the matplotlib report is from February 2018, and refers to pytrainer, which i also use, and does not open anymore