Matplotlib 3.1.0: KeyError 'back' in NavigationToolbar

[chipmuenk]

Running pyfda with matplotlib 3.1.0 yields the following error (which doesn't happen under matplotlib 3.0.3):

Python: 3.7.3
pyQt: 5.9.2
Anaconda distribution, Ubuntu 18.04 64 bit

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(base) cmuenker@cmuenker-TUXEDO:~/Daten/design/python/git/pyfda/pyfda/plot_widgets$ python -m pyfda.plot_widgets.plot_phi
Traceback (most recent call last):
File "/home/cmuenker/anaconda3/lib/python3.7/runpy.py", line 193, in _run_module_as_main
"main", mod_spec)
File "/home/cmuenker/anaconda3/lib/python3.7/runpy.py", line 85, in _run_code
exec(code, run_globals)
File "/home/cmuenker/Daten/design/python/git/pyfda/pyfda/plot_widgets/plot_phi.py", line 233, in
main()
File "/home/cmuenker/Daten/design/python/git/pyfda/pyfda/plot_widgets/plot_phi.py", line 227, in main
mainw = Plot_Phi(None)
File "/home/cmuenker/Daten/design/python/git/pyfda/pyfda/plot_widgets/plot_phi.py", line 37, in init
self._construct_UI()
File "/home/cmuenker/Daten/design/python/git/pyfda/pyfda/plot_widgets/plot_phi.py", line 106, in _construct_UI
self.mplwidget = MplWidget(self)
File "/home/cmuenker/Daten/design/python/git/pyfda/pyfda/plot_widgets/mpl_widget.py", line 90, in init
self.mplToolbar = MplToolbar(self.pltCanv, self) # inherits all methods
File "/home/cmuenker/Daten/design/python/git/pyfda/pyfda/plot_widgets/mpl_widget.py", line 233, in init
NavigationToolbar.init(self, *args, **kwargs)
File "/home/cmuenker/anaconda3/lib/python3.7/site-packages/matplotlib/backends/backend_qt5.py", line 685, in init
NavigationToolbar2.init(self, canvas)
File "/home/cmuenker/anaconda3/lib/python3.7/site-packages/matplotlib/backend_bases.py", line 2638, in init
self.set_history_buttons()
File "/home/cmuenker/anaconda3/lib/python3.7/site-packages/matplotlib/backends/backend_qt5.py", line 854, in set_history_buttons
self._actions['back'].setEnabled(can_backward)
KeyError: 'back'

[chipmuenk]

Appearently, this is fixed in Matplotlib 3.1.1 (matplotlib/matplotlib#14319).