Override a Qt MouseEvent but only if class variable is True

Question

I have QComboBox that I want the user to be able to lock the index of. To do this I subclassed QComboBox and overrode the mousePressEvent to be empty, but inside a method for QComboBox.

Two problems with what I tried:

• I can't figure out how to re-define mousePressEvent inside another class method
• I don't know how to restore the original mousePressEvent behavior of a QComboBox if a certain condition is not met. My code:

class MyComboBox(QtWidgets.QComboBox):
    def __init__(self, *args, **kwargs):
        super(self.__class__, self).__init__(*args, **kwargs)

    def lockSelection(self, bool=None):
        if bool:
            def mousePressEvent(self, *args, **kwargs):
                pass
        else:
            def mousePressEvent(self, *args, **kwargs):
                return QtWidgets.QComboBox.mousePressEvent(*args, **kwargs)

..... later

## I want this to get my overriden mousePressEvent 

MyComboBox.lockSelection(True)

## I want this to get the original mousePressEvent

MyComboBox.lockSelection(False)

Answer 1

If you want to block an inherited method you just have to override the method and avoid calling the method when necessary:

from PyQt5 import QtWidgets


class MyComboBox(QtWidgets.QComboBox):
    def lockSelection(self, lock):
        self._lock_selection = lock

    def mousePressEvent(self, event):
        lock = getattr(self, "_lock_selection", False)
        if not lock:
            super(MyComboBox, self).mousePressEvent(event)


if __name__ == "__main__":
    import sys

    app = QtWidgets.QApplication(sys.argv)

    w = QtWidgets.QWidget()

    combo = MyComboBox()
    combo.addItems(list("ABCD"))

    radio = QtWidgets.QCheckBox("Lock")
    radio.toggled.connect(combo.lockSelection)

    lay = QtWidgets.QHBoxLayout(w)
    lay.addWidget(radio)
    lay.addWidget(combo)
    w.resize(320, 60)
    w.show()
    sys.exit(app.exec_())

If you want to avoid inheritance you can implement a locker using an event filter so you can use it in any widget:

from PyQt5 import QtCore, QtWidgets


class MouseLocker(QtCore.QObject):
    def __init__(self, widget):
        super(MouseLocker, self).__init__(widget)
        widget.installEventFilter(self)
        self._lock_selection = False

    def lockSelection(self, lock):
        self._lock_selection = lock

    def eventFilter(self, obj, event):
        if obj is self.parent() and event.type() == QtCore.QEvent.MouseButtonPress:
            return self._lock_selection
        return super(MouseLocker, self).eventFilter(obj, event)


if __name__ == "__main__":
    import sys

    app = QtWidgets.QApplication(sys.argv)

    w = QtWidgets.QWidget()

    combo = QtWidgets.QComboBox()
    combo.addItems(list("ABCD"))
    locker = MouseLocker(combo)

    radio = QtWidgets.QCheckBox("Lock")
    radio.toggled.connect(locker.lockSelection)

    lay = QtWidgets.QHBoxLayout(w)
    lay.addWidget(radio)
    lay.addWidget(combo)
    w.resize(320, 60)
    w.show()
    sys.exit(app.exec_())