Segmentation fault on Ubuntu 13.10 when using guiqwt

[Ningfei Li]

Ubuntu 13.10
Package: python-qt4 (4.10.3-1ubuntu1)
Package: python-sip (4.15.2-1ubuntu1)

In Python, when I tried "guiqwt.tests.run()" and ran any script with plot function in it, it would cause the segmentation fault. But when I revert python-qt4 adn python-sip to the version in Ubuntu 13.04: python-qt4 (4.10-0ubuntu3) ) and python-sip (4.14.5-0ubuntu1), everything works fine.

I traced the bug, found that: with new version of python-qt4 and python-sip, the guiqwt script will stuck there in this line: self.emit(SIG_PLOT_LABELS_CHANGED, self).

After googling it, I find this segfault problem also affect some other users/packages:
https://bbs.archlinux.org/viewtopic.php?id=168667
https://bugs.archlinux.org/task/36652

So this seems not a bug of python-guiqwt but a build problem with the python-qt4 and python-sip.

I tried to build latest snapshot version of PyQt and sip and install them locally. But this seg fault still exist.

[Scott Kitterman (kitterman)]

Try rebuilding python-guiqwt. I think it will work then.

[Ningfei Li (ningfei)]

@Scott

Thanks for your reply!
Since python-guiqwt is almost a pure python package. I don't think a rebuilding will work. I had tried it and still got that segfault.

If you step into the code when you plot, you will find that the script stucks there at this line:
self.emit(SIG_PLOT_LABELS_CHANGED, self) in baseplot.py (in python-guiqwt directory). "self" here is a BasePlot class inherited from QwtPlot. And QwtPlot is imported as this : from PyQt4.Qwt5 import QwtPlot. I also tried to rebuild python-qwt5-qt4. But segfault again...

The signal SIG_PLOT_LABELS_CHANGED here is import from signal.py (also in python-guiqwt directory): SIG_PLOT_LABELS_CHANGED = SIGNAL('plot_labels_changed(PyQt_PyObject)').

The SIGNAL here is import via this: from guidata.qt.QtCore import SIGNAL. Here the python-guidata is also a pure python package, in which there exist a script QtCore.py with the following lines that might be related:
from PyQt4.QtCore import *
from PyQt4.QtCore import pyqtSignal as Signal

So that's why I think it can be a upstream problem with pyqt4...

[Scott Kitterman (kitterman)]

OK. Thanks for the analysis. If you can extract a reduced test case that
demonstrates the problem, I'll send it upstream to see about a fix.

[Ningfei Li (ningfei)]

Hi Scott,

Thanks again for your quick reply! Here I can give a short test script to reproduce this problem (as in attachment).
It's basically a test case provided in guiqwt.tests (histogram.py).
During debugging, it will stucks at line 12: win = CurveDialog(edit=False, toolbar=True, wintitle="Histogram test")
Then you trace into it to plot.py, curve.py and then baseplot.py. Finally you will be here in baseplot.py: self.emit(SIG_PLOT_LABELS_CHANGED, self) in function: def update_axis_style(self, axis_id)

Package: python-qt4 (4.10.3-1ubuntu1)
Package: python-sip (4.15.2-1ubuntu1)

reverting to python-qt4 (4.10-0ubuntu3) ) and python-sip (4.14.5-0ubuntu1) then everything works fine.

[Ningfei Li (ningfei)]

Hi Scott,

I just find a fixed package here: https://bugs.launchpad.net/ubuntu/+source/pyqwt5/+bug/1243102 that solves my problem!
It seems it's a problem with python-qwt5-qt4 rather than python-qt4. At least my guiqwt package works fine now.