Qt5Agg backend can't be used

[b3nmore]

The current version from yakkety (1.5.2~rc2-1) does not work with pyqt5. Trying to plot to the Qt5Agg backend raises the following error:
QObject::connect: Cannot connect NavigationToolbar2QT::message(QString) to (null)::_show_message()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python3/dist-packages/matplotlib/pyplot.py", line 3146, in plot
    ax = gca()
  File "/usr/lib/python3/dist-packages/matplotlib/pyplot.py", line 928, in gca
    return gcf().gca(**kwargs)
  File "/usr/lib/python3/dist-packages/matplotlib/pyplot.py", line 578, in gcf
    return figure()
  File "/usr/lib/python3/dist-packages/matplotlib/pyplot.py", line 527, in figure
    **kwargs)
  File "/usr/lib/python3/dist-packages/matplotlib/backends/backend_qt5agg.py", line 43, in new_figure_manager
    return new_figure_manager_given_figure(num, thisFig)
  File "/usr/lib/python3/dist-packages/matplotlib/backends/backend_qt5agg.py", line 51, in new_figure_manager_given_figure
    return FigureManagerQT(canvas, num)
  File "/usr/lib/python3/dist-packages/matplotlib/backends/backend_qt5.py", line 465, in __init__
    self.toolbar.message.connect(self._show_message)
TypeError: connect() failed between NavigationToolbar2QT.message[str] and _show_message()

This bug is fixed upstream and was backported to 1.5.x (https://github.com/matplotlib/matplotlib/pull/6854). It is also fixed in debian testing (https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=835455).

[Launchpad Janitor (janitor)]

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