python - Dedenting function in QPlainTextEdit causes segfault if last line is involved -

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i'm working on source code editor should have smart indent/dedent behaviour. however, dedenting method seems causing segmentation fault. i'd pleased if work out why.

here's minimal example:

#!/usr/bin/env python import sip sip.setapi('qstring', 2) sip.setapi('qvariant', 2) pyqt4 import qtgui pyqt4.qtcore import qt class editor(qtgui.qplaintextedit):     def keypressevent(self, event):         key = event.key()         if key == qt.key_backtab:             cursor = self.textcursor()             start, end = cursor.selectionstart(), cursor.selectionend()             cursor.begineditblock()             b = self.document().findblock(start)             while b.isvalid() , b.position() <= end:                 t = b.text()                 p1 = b.position()                 p2 = p1 + min(4, len(t) - len(t.lstrip()))                 cursor.setposition(p1)                 cursor.setposition(p2, qtgui.qtextcursor.keepanchor)                 cursor.removeselectedtext()                 b = b.next()             cursor.endeditblock()         else:             super(editor, self).keypressevent(event) class window(qtgui.qmainwindow):     """     new gui editing ``.mmt`` files.     """     def __init__(self, filename=none):         super(window, self).__init__()         self.e = editor()         self.e.setplaintext('line 1\n    line 2\n    line 3')         self.setcentralwidget(self.e)         self.e.setfocus() if __name__ == '__main__':     = qtgui.qapplication([])     w = window()     w.show()     a.exec_()

to recreate, make selection starting on second line , ending on third line, press shift+tab dedent , end trigger segfault.

platform:

  • running on fedora (linux)
  • python 2.7.8 (default, nov 10 2014, 08:19:18) [gcc 4.9.2 20141101 (red hat 4.9.2-1)]
  • pyqt 4.8.6 (but happens in pyside too)

update:

thanks

it seems bug in qt:

https://bugreports.qt.io/browse/qtbug-30051

apparently editing multiple blocks within qtextcursor.begineditblock() causes last block's layout break, in case causing segfault.

a work-around may rewrite dedenting code single operation (determine text after dedenting, delete selected lines, replace new text)

if knows better workaround, please let me know!


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