python segfaulting, MemoryError (PyQt)

[Denis L]

"Phil Thompson" <phil at riverbankcomputing.com> wrote in message 
news:mailman.4690.1240925876.11746.python-list at python.org...
> On Tue, 28 Apr 2009 14:54:41 +0200, "Denis L" <no at spam.com> wrote:
>> "Phil Thompson" <phil at riverbankcomputing.com> wrote in message
>> news:mailman.4664.1240907352.11746.python-list at python.org...
>>> On Tue, 28 Apr 2009 03:53:34 +0200, "Denis L" <no at spam.com> wrote:
>>>> Hello,
>>>>
>>>> I'm experiencing odd errors on both windows and linux with the
> following
>>>> code:
>>>>
>>>> import sys
>>>> from PyQt4.QtCore import *
>>>> from PyQt4.QtGui import *
>>>>
>>>> class Options(QDialog):
>>>>     def __init__(self, values):
>>>>         QDialog.__init__(self)
>>>>
>>>>         self.values = values
>>>>
>>>>         fooEdit = QLineEdit(values['foo'])
>>>>         self.connect(fooEdit, SIGNAL('textChanged(QString)'),
>>>>                      lambda value: self.optionChanged('foo', value))
>>>>
>>>>         barEdit = QLineEdit(values['bar'])
>>>>         self.connect(barEdit, SIGNAL('textChanged(QString)'),
>>>>                      lambda value: self.optionChanged('bar', value))
>>>>
>>>>         layout = QVBoxLayout()
>>>>         layout.addWidget(fooEdit)
>>>>         layout.addWidget(barEdit)
>>>>
>>>>         self.setLayout(layout)
>>>>
>>>>     def optionChanged(self, option, value):
>>>>         self.values[option] = value
>>>>         print self.values
>>>>
>>>> def main(args):
>>>>     app = QApplication(args)
>>>>     values = dict(foo='', bar='')
>>>>     dialog = Options(values)
>>>>     dialog.show()
>>>>     app.exec_()
>>>>
>>>> if __name__ == '__main__':
>>>>     main(sys.argv)
>>>>
>>>>
>>>> If I type a character in fooEdit, another character in barEdit, and
> then
>>>> delete the character from barEdit I get an unhandled win32 exception
>>>> occured
>>>> in python.exe on windows and segfault on linux.
>>>>
>>>> If I type a character in fooEdit, delete it, and then type a character
>>>> in
>>>
>>>> barEdit I get:
>>>>
>>>> {'foo': PyQt4.QtCore.QString(u'a'), 'bar': ''}
>>>> {'foo': PyQt4.QtCore.QString(u''), 'bar': ''}
>>>> {'foo': Traceback (most recent call last):
>>>>   File "L:\home\dev\python\test.py", line 17, in <lambda>
>>>>     lambda value: self.optionChanged('bar', value))
>>>>   File "L:\home\dev\python\test.py", line 27, in optionChanged
>>>>     print self.values
>>>> MemoryError
>>>>
>>>> I'm using Python 2.5.4 and PyQt 4.4.3-1
>>>>
>>>> Thanks in advance for any help.
>>>
>>> Works fine for me with current versions.
>>>
>>> Phil
>>
>> I have noticed that if I do "self.values[option] = QString(value)"
>> instead of "self.values[option] = value" in optionChanged I don't get any
>
>> errors.
>>
>> Is it perhaps not safe to keep the reference to the lambda QString
>> argument?
>
> It shouldn't make any difference.
>
> Phil

Last idea, C++ declaration of textChanged signal is this:

void textChanged (const QString&text)

would self.values[option] = value store the reference to QString? And if so 
is that safe, to access that object after my slot returns?

As far as I can see C++ equivalent would be

QString* pointer = &text; then derferencing that pointer later in the code. 
I can see how this could cause problems.

Btw you are using PyQt 4.4.4 correct? What version of python?