Qt5 backend doesn't work with Qt 5.3

[jenshnielsen]

I have previously had the Qt5 backend working with mpl 1.4.0 however It seems broken to me now.
Trying to do a simple plot with plt.plot results in

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-4-bf7ca2578bf6> in <module>()
----> 1 plt.plot(range(100))

/usr/local/Cellar/python3/3.4.1_1/Frameworks/Python.framework/Versions/3.4/lib/python3.4/site-packages/matplotlib-1.5.x-py3.4-macosx-10.9-x86_64.egg/matplotlib/pyplot.py in plot(*args, **kwargs)
   3089 @_autogen_docstring(Axes.plot)
   3090 def plot(*args, **kwargs):
-> 3091     ax = gca()
   3092     # allow callers to override the hold state by passing hold=True|False
   3093     washold = ax.ishold()

/usr/local/Cellar/python3/3.4.1_1/Frameworks/Python.framework/Versions/3.4/lib/python3.4/site-packages/matplotlib-1.5.x-py3.4-macosx-10.9-x86_64.egg/matplotlib/pyplot.py in gca(**kwargs)
    826     matplotlib.figure.Figure.gca : The figure's gca method.
    827     """
--> 828     ax =  gcf().gca(**kwargs)
    829     return ax
    830

/usr/local/Cellar/python3/3.4.1_1/Frameworks/Python.framework/Versions/3.4/lib/python3.4/site-packages/matplotlib-1.5.x-py3.4-macosx-10.9-x86_64.egg/matplotlib/pyplot.py in gcf()
    460         return figManager.canvas.figure
    461     else:
--> 462         return figure()
    463
    464 fignum_exists = _pylab_helpers.Gcf.has_fignum

/usr/local/Cellar/python3/3.4.1_1/Frameworks/Python.framework/Versions/3.4/lib/python3.4/site-packages/matplotlib-1.5.x-py3.4-macosx-10.9-x86_64.egg/matplotlib/pyplot.py in figure(num, figsize, dpi, facecolor, edgecolor, frameon, FigureClass, **kwargs)
    433                                         frameon=frameon,
    434                                         FigureClass=FigureClass,
--> 435                                         **kwargs)
    436
    437         if figLabel:

/usr/local/Cellar/python3/3.4.1_1/Frameworks/Python.framework/Versions/3.4/lib/python3.4/site-packages/matplotlib-1.5.x-py3.4-macosx-10.9-x86_64.egg/matplotlib/backends/backend_qt5agg.py in new_figure_manager(num, *args, **kwargs)
     46     FigureClass = kwargs.pop('FigureClass', Figure)
     47     thisFig = FigureClass(*args, **kwargs)
---> 48     return new_figure_manager_given_figure(num, thisFig)
     49
     50

/usr/local/Cellar/python3/3.4.1_1/Frameworks/Python.framework/Versions/3.4/lib/python3.4/site-packages/matplotlib-1.5.x-py3.4-macosx-10.9-x86_64.egg/matplotlib/backends/backend_qt5agg.py in new_figure_manager_given_figure(num, figure)
     53     Create a new figure manager instance for the given figure.
     54     """
---> 55     canvas = FigureCanvasQTAgg(figure)
     56     return FigureManagerQT(canvas, num)
     57

/usr/local/Cellar/python3/3.4.1_1/Frameworks/Python.framework/Versions/3.4/lib/python3.4/site-packages/matplotlib-1.5.x-py3.4-macosx-10.9-x86_64.egg/matplotlib/backends/backend_qt5agg.py in __init__(self, figure)
    179         if DEBUG:
    180             print('FigureCanvasQtAgg: ', figure)
--> 181         FigureCanvasQT.__init__(self, figure)
    182         FigureCanvasAgg.__init__(self, figure)
    183         self._drawRect = None

/usr/local/Cellar/python3/3.4.1_1/Frameworks/Python.framework/Versions/3.4/lib/python3.4/site-packages/matplotlib-1.5.x-py3.4-macosx-10.9-x86_64.egg/matplotlib/backends/backend_qt5.py in __init__(self, figure)
    235         # __init__() takes exactly 2 arguments (1 given) on QWidget
    236         # PyQt5
--> 237         super(FigureCanvasQT, self).__init__(figure=figure)
    238         self.figure = figure
    239         self.setMouseTracking(True)

TypeError: 'figure' is an unknown keyword argument

This is naturally because QtWidgets.QWidget does not take a figure keyword argument. Removing the kwarg seems to resolve the issue with a simple figure. But I am unsure if the intention of this line is to call init on QtWidgets.QWidget or FigureCanvasBase which does take that kwarg.

Since this has working before I guess that this is somehow related to me upgrading to Qt5.3.
The traceback above is from the master branch but the same seems to happen with 1.4.0

[jenshnielsen]

The QT4 backend explicitly calls init on both of the parent classes:

# Note different super-calling style to backend_qt5
QtWidgets.QWidget.__init__(self)
FigureCanvasBase.__init__(self, figure)

@mfitzp can you remember why this difference exists between the Qt4 and Qt5 backends

[mfitzp]

@jenshnielsen If I remember correctly, the Qt5 backend uses super() because otherwise it wouldn't work. The init handling in PyQt5 was fixed so that super works as it should with QObject but the side effect seemed to be that it then didn't work by calling FigureCanvasBase.__init__() directly.

You're correct that the figure parameter is supposed to be going to FigureCanvasBase.

Can you give me some details of your system/setup so I can reproduce?

[jenshnielsen]

This is on a Mac OSX 10.9 with Qt5.3.2, PyQt5 5.3.2 and python 3.4 from Homebrew as well.

I know that the backend used to work for me before so I am guessing that this is somehow related to me upgrading to QT5.3 but I haven't tried reinstalling Qt5.2

My understanding of super is that in this context it will call init() on the first class that is inherited from i.e. QtWidgets.QWidget but not on FigureCanvasBase.

[jenshnielsen]

I can confirm that I see the issue that you describe when explicitly initialize the parent classes on Ubuntu 14.04 with Qt 5.2 ...

When explicitly calling QtWidgets.QWidget.init(self) it complains about missing figure. When calling QtWidgets.QWidget.init(self, figure=figure) it complains that figure is an unknown kwarg. I think there is a deeper issue here.

[stonebig]

I was hoping Matplotlib 1.4.1 would be out "by October 1rst".
Has someone a new Forecast of release date ? (users are out in the cold with 1.4.0)

[tacaswell]

@stonebig If you really need something that has been fixed on 1.4.x install from source. We have a couple of blocking issues left (take a look at the 1.4.1 milestone), an rc will be tagged once they are cleaned up. If you have spare cycles any help sorting those issues out would be appreciated.

[stonebig]

hi @tacaswell ,

I'm relying on matplotlib versions (or releases candidates), as distributed by Christoph Gohlke, so it's a break for me to grab the latest source.
I could do what you suggest without blinking, IF Matplotlib was a pure python project, but github statistic states it is only a 87.3% python project.
(life is not as easy for python windows users as it is for linux ones)

[jenshnielsen]

Ok, This actually doesn't have anything to do with qt 5.3

What happens is that I have the env variable QT_API set to pyqt

That results in pyqt4 being imported even within the qt5 backend which causes this issue.

[tacaswell]

re-labeled this as not-a-blocker as it seems to be a configuration issue.

[jenshnielsen]

I would disagree on this being a config issue. It makes no sense for the matplotlib qt5 backend to be broken in a strange and hard to debug way just because I have set a variable to determine which qt4 library to use in the qt4 backend and in mayavi. The result of the current code is that matplotlib actually imports pyqt4 into the qt5 backend which imho is a clear bug.