Plotting error with ipympl 0.5 series

Trying to do interactive plotting with the hyperspy library, users have recently (the last two weeks) started experiencing the following bug when we try to plot after upgrading ipympl. The following fails with %matplotlib widget, but works with %matplotlib notebook. (This is not testable with lab, since the notebook backend doesn’t work there.)

Since it only started happening recently (and we didn’t update hyperspy), I believe something has changed in the recent versions of ipympl that broke it for us. If the implemented change is for the better, we would be happy to change our code, but I’m not sure what has changed.

# The following works if we replace widget with notebook
%matplotlib widget
import hyperspy.api as hs

s = hs.signals.Signal1D([1,2,3])
s.plot()

This is the expected plot:

The error is the (long) following:

---------------------------------------------------------------------------
IndexError                                Traceback (most recent call last)
<ipython-input-3-886abc61b753> in <module>
----> 1 s.plot()

c:\users\thomasaar\documents\github\hyperspy\hyperspy\signal.py in plot(self, navigator, axes_manager, plot_markers, **kwargs)
   2158                     " \"slider\", None, a Signal instance")
   2159 
-> 2160         self._plot.plot(**kwargs)
   2161         self.events.data_changed.connect(self.update_plot, [])
   2162         if self._plot.signal_plot:

c:\users\thomasaar\documents\github\hyperspy\hyperspy\drawing\mpl_he.py in plot(self, **kwargs)
    174                 self.pointer.connect_navigate()
    175             self.plot_navigator(**kwargs.pop('navigator_kwds', {}))
--> 176         self.plot_signal(**kwargs)
    177 
    178     def assign_pointer(self):

c:\users\thomasaar\documents\github\hyperspy\hyperspy\drawing\mpl_hse.py in plot_signal(self, **kwargs)
    124 
    125         self.signal_plot = sf
--> 126         sf.plot(**kwargs)
    127         if sf.figure is not None:
    128             if self.axes_manager.navigation_axes:

c:\users\thomasaar\documents\github\hyperspy\hyperspy\drawing\signal1d.py in plot(self, data_function_kwargs, **kwargs)
    135                 # complains
    136                 pass
--> 137         self.figure.canvas.draw()
    138 
    139     def _on_close(self):

~\.conda\envs\py5\lib\site-packages\matplotlib\backends\backend_webagg_core.py in draw(self)
    149         self._png_is_old = True
    150         try:
--> 151             super().draw()
    152         finally:
    153             self.manager.refresh_all()  # Swap the frames.

~\.conda\envs\py5\lib\site-packages\matplotlib\backends\backend_agg.py in draw(self)
    388         self.renderer = self.get_renderer(cleared=True)
    389         # Acquire a lock on the shared font cache.
--> 390         with RendererAgg.lock, \
    391              (self.toolbar._wait_cursor_for_draw_cm() if self.toolbar
    392               else nullcontext()):

~\.conda\envs\py5\lib\contextlib.py in __enter__(self)
    111         del self.args, self.kwds, self.func
    112         try:
--> 113             return next(self.gen)
    114         except StopIteration:
    115             raise RuntimeError("generator didn't yield") from None

~\.conda\envs\py5\lib\site-packages\matplotlib\backend_bases.py in _wait_cursor_for_draw_cm(self)
   2771         if self._draw_time - last_draw_time > 1:
   2772             try:
-> 2773                 self.set_cursor(cursors.WAIT)
   2774                 yield
   2775             finally:

~\.conda\envs\py5\lib\site-packages\matplotlib\backends\backend_webagg_core.py in set_cursor(self, cursor)
    379     def set_cursor(self, cursor):
    380         if cursor != self.cursor:
--> 381             self.canvas.send_event("cursor", cursor=cursor)
    382         self.cursor = cursor
    383 

~\.conda\envs\py5\lib\site-packages\matplotlib\backends\backend_webagg_core.py in send_event(self, event_type, **kwargs)
    344 
    345     def send_event(self, event_type, **kwargs):
--> 346         self.manager._send_event(event_type, **kwargs)
    347 
    348 

~\.conda\envs\py5\lib\site-packages\matplotlib\backends\backend_webagg_core.py in _send_event(self, event_type, **kwargs)
    487         payload = {'type': event_type, **kwargs}
    488         for s in self.web_sockets:
--> 489             s.send_json(payload)
    490 
    491 

~\.conda\envs\py5\lib\site-packages\ipympl\backend_nbagg.py in send_json(self, content)
    207         if content['type'] == 'cursor':
    208             cursors = ['pointer', 'default', 'crosshair', 'move']
--> 209             self._cursor = cursors[content['cursor']]
    210 
    211         elif content['type'] == 'message':

IndexError: list index out of range

[thomasaarholt]

Excellent work! Thanks @martinRenou!

[martinRenou]

I just released the Python package, 0.5.4 should be available via pip now. Coming soon via conda.