PySide segfaults immediately on Linux

[mdboom]

PySide 1.1.0 crashes upon startup with this script

import matplotlib
matplotlib.use('Qt4Agg')
matplotlib.rcParams['backend.qt4']='PySide'
from matplotlib import pyplot
pyplot.plot()
pyplot.show()

It may or may not be related to #1323. (It happens whether or not that patch is applied).

[pelson]

@mdboom : I've put a release critical label on this (If you don't agree, feel free to take it off).

[dmcdougall]

I can't test this; I don't have a linux machine.

[mdboom]

@pelson: I agree it's release critical. Thanks for that.

[mdboom]

I think I have a fix here. When it tries to set the cursor shape globally for the application, it was crashing. Setting the cursor only for the window (and not the app as a whole) mysteriously resolves the issue. Would those on a Mac mind testing this (with both PyQt4 and PySide)?

[efiring]

With PySide 1.1.2 on OSX 10.8, your test script above works OK with or without this change.

Setting the cursor only for the window seems like the right thing to do in any case, doesn't it?

[mdboom]

Yes -- I think this is more "expected" in any event.

[mdboom]

Also, can you confirm it doesn't break if you use PyQt4 instead of PySide? They both use the same backend code (only with different imports).

[efiring]

On 2012/10/16 7:42 AM, Michael Droettboom wrote:

Also, can you confirm it doesn't break if you use PyQt4 instead of
PySide? They both use the same backend code (only with different imports).

PyQt4 also works.

[dmcdougall]

PyQt4 also works.

Same here. OS X 10.7 python 2.7.3.

[mdboom]

Great! I'm going to go ahead and merge, then.

[ChrisBeaumont]

Hi @mdboom et al,

I noticed that this change broke code I was using that instantiated a FigureCanvas outside of pyplot. My problem is that canvas.manager is added to a FigureCanvas from FigureManagerBase (https://github.com/matplotlib/matplotlib/blob/master/lib/matplotlib/backend_bases.py#L2454). I hadn't created a FigureManager so, when matplotlib tries to change the cursor, python cant find canvas.manager and raises an attribute error:

--> 606         self.canvas.manager.window.setCursor(cursord[cursor])
AttributeError: 'MplCanvas' object has no attribute 'manager'

The documentation of FigureManagerBase says it is a "helper class for pyplot mode". Are FigureCanvases used outside of pyplot supposed to have a manager attribute? If so, should that be added to the FigureCanvas.init
somehow? If not, can this fix be modified to not depend on manager?

I can solve my own problem user-side, by creating a manager. I'm just posting here in case this behavior is unintended.

[ChrisBeaumont]

One solution that I think does the same thing:

self.canvas.window().setCursor(cursord[cursor])

since Qt FigureCanvases are QWidgets