Qt method override.

def keyPressEvent(self, event):
        """Qt method override."""
        event_key = event.key()
        if not event_key or event_key == Qt.Key_unknown:
            return
        if len(self._qsequences) == 4:
            # QKeySequence accepts a maximum of 4 different sequences.
            return
        if event_key in [Qt.Key_Control, Qt.Key_Shift,
                         Qt.Key_Alt, Qt.Key_Meta]:
            # The event corresponds to just and only a special key.
            return

        translator = ShortcutTranslator()
        event_keyseq = translator.keyevent_to_keyseq(event)
        event_keystr = event_keyseq.toString(QKeySequence.PortableText)
        self._qsequences.append(event_keystr)
        self.update_warning()