I've tried to connect an instance method as a new-style signal callback. This
works if I do nothing else, but if I happen to call a numpy method after
connecting the callback, I get an error from PyQt, but during the numpy call:
Traceback (most recent call last):
File "signal_bug.py", line 30, in <module>
main()
File "signal_bug.py", line 24, in main
nqo = NotQObject(slider)
File "signal_bug.py", line 14, in __init__
a = numpy.arange(10).max()
TypeError: NotQObject cannot be converted to PyQt4.QtCore.QObject in this
context
There are some places in numpy where we check to see if anyone has set an
exception. I suspect that what is happening is that PyQt is checking if the
"self" on the bound instancemethod callback is a QObject in order to go down one
path and otherwise go down another and failing to clear up this exception before
returning control. I am using PyQt4 4.5 on OS X and trunk numpy, but I suspect
any numpy will do. I am downloading 4.5.2 now to see if this has been fixed in
the meantime, but I do not see anything in the changelog that looks promising.
import sys
from PyQt4 import QtGui
import numpy
class NotQObject(object):
""" Definitely not a QObject.
"""
def __init__(self, slider):
self.slider = slider
self.slider.valueChanged.connect(self.on_value_changed)
a = numpy.arange(10).max()
def on_value_changed(self, ival):
print ival
def main():
app = QtGui.QApplication(sys.argv)
slider = QtGui.QSlider()
nqo = NotQObject(slider)
app.exec_()
if __name__ == '__main__':
main()
--
Robert Kern
"I have come to believe that the whole world is an enigma, a harmless enigma
that is made terrible by our own mad attempt to interpret it as though it had
an underlying truth."
-- Umberto Eco
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