PyQt keyPressEvent not triggered from QDialog - python-3.x

Question

I have a simple example of of a dialog window that has the keyPressEvent method. However, no matter what is typed when the sub window has focus, the event is not triggered.
import sys
from PyQt4.QtCore import *
from PyQt4.QtGui import *
import PyQt4.Qt
class KpeWindow(QDialog):
def __init__(self, parent=None):
super().__init__(parent)
main = QVBoxLayout(self)
label = QLabel(self)
label.setText('Test the keyPressEvent')
self.adjustSize()
self.setLayout(main)
def keyPressEvent(self, event):
QMessageBox.warning(self, 'MDI', 'keyPressEvent')
super().keyPressEvent(event)
class MainWindow(QMainWindow):
def __init__(self):
super().__init__()
self.setWindowTitle('KeyPressEvent Test')
child = KpeWindow()
self.setCentralWidget(child)
if __name__ == '__main__':
app = QApplication(sys.argv)
mainWin = MainWindow()
mainWin.show()
sys.exit(app.exec_())

Answer 1

The following code works:
class KpeWindow(QWidget):
def __init__(self, parent=None):
QWidget.__init__(self,parent)
main = QVBoxLayout(self)
label = QLabel(self)
label.setText('Test the keyPressEvent')
main.addWidget(label)
self.adjustSize()
self.setLayout(main)
def keyPressEvent(self, event):
QMessageBox.warning(self, 'MDI', 'keyPressEvent')
self.parent().keyPressEvent(event)
class MainWindow(QMainWindow):
def __init__(self):
QMainWindow.__init__(self)
self.setWindowTitle('KeyPressEvent Test')
main = QVBoxLayout(self)
child = KpeWindow(self)
child.setFocusPolicy(Qt.StrongFocus)
self.setFocusProxy(child)
main.addWidget(child)
child.setFocus(True)
self.adjustSize()
self.setLayout(main)
I am not sure which of my changes work, I suspect setFocusProxy. In general I would recommend using QWidget as the child, and putting things into layouts even when there are no siblings.

Answer 2

The keyPressEvent is sensitive to the focus policy. In your example, the event is going to the QMainWindow (if you move the keyPressEvent to there, it does receive key events).
Is there any reason to have a dialog within a window? If you launch the dialog in the usual way, using child.show(), child.exec_() instead of setCentralWidget, it shows in a separate window and captures the key event.