Handle arrow key events by setting the focus policy - pyqt

Question

I want to handle key events of the arrow keys in my application. I have already read that for doing so the focus must be disabled. I follow this method: PyQt not recognizing arrow keys. Indeed, when calling self.setChildrenFocusPolicy(QtCore.Qt.NoFocus) (as defined in the linked thread and in my source code below) within MyApp.__init__, hitting an arrow key raises a key event. However, I do not want to keep the focus disabled during the entire runtime of the application but only upon clicking a button. So I move self.setChildrenFocusPolicy(QtCore.Qt.NoFocus) to the button click function:
def __init__(self):
self.pushButton.clicked.connect(self.pushButtonClicked)
def pushButtonClicked(self):
self.setChildrenFocusPolicy(QtCore.Qt.NoFocus)
Indeed, hitting the push button disables the focus (e.g. a line edit cannot take the text cursor anymore). However, hitting an arrow key still does not raise a key event.
The whole application (you will need a mainwindow.ui with a push button):
import sys
from PyQt4 import QtCore, QtGui, uic
qtCreatorFile = "d:/test/mainwindow.ui"
Ui_MainWindow, QtBaseClass = uic.loadUiType(qtCreatorFile)
class MyApp(QtGui.QMainWindow, Ui_MainWindow):
def setChildrenFocusPolicy(self, policy):
def recursiveSetChildFocusPolicy (parentQWidget):
for childQWidget in parentQWidget.findChildren(QtGui.QWidget):
childQWidget.setFocusPolicy(policy)
recursiveSetChildFocusPolicy(childQWidget)
recursiveSetChildFocusPolicy(self)
def __init__(self):
QtGui.QMainWindow.__init__(self)
Ui_MainWindow.__init__(self)
self.setupUi(self)
self.pushButton.clicked.connect(self.pushButtonClicked)
def pushButtonClicked(self):
self.setChildrenFocusPolicy(QtCore.Qt.NoFocus)
def keyPressEvent(self, event):
print "a"
if __name__ == "__main__":
app = QtGui.QApplication(sys.argv)
window = MyApp()
window.show()
sys.exit(app.exec_())

Answer 1

There's no need to disable focus. You can get access to all key events by installing an event filter on the application:
class MyApp(QtGui.QMainWindow, Ui_MainWindow):
def __init__(self):
...
QtGui.qApp.installEventFilter(self)
def eventFilter(self, source, event):
if event.type() == QtCore.QEvent.KeyPress:
print(event.key())
return super(MyApp, self).eventFilter(source, event)
But note that this really does get everything, so you may end up with more than you bargained for...