Ability to disable QCheckbox if two other QCheckboxes are selected

Question

I have 3 checkboxes that I have created in Designer using PyQt5. I am wanting to have the logic flow like this:

If any of the 2 checkboxes are checked, disable the last remaining checkbox. Once a checkbox is unchecked, the disabled checkbox should be re-enabled and so forth.

The "any of the 2 checkboxes are checked" is the part I am struggling with because I don't want to have a bunch of if statements creating this logic.

Here is my code thus far:

class MyApp(QtWidgets.QMainWindow, Ui_MainWindow):
    def __init__(self):
        QtWidgets.QMainWindow.__init__(self)
        Ui_MainWindow.__init__(self)
        self.setFixedSize(250, 330)
        self.setupUi(self)

        self.sewage.stateChanged.connect(self.onStateChange)
        self.water.stateChanged.connect(self.onStateChange)
        self.internet.stateChanged.connect(self.onStateChange)

    @pyqtSlot(int)
    def onStateChange(self, state):
        if state == Qt.Checked:
            if self.sender() == self.sewage or self.sender() == self.internet:
                self.water.setEnabled(False)
            elif self.sender() == self.internet or self.sender() == self.water:
                self.sewage.setEnabled(False)
            elif self.sender() == self.water or self.sender() == self.sewage:
                self.internet.setEnabled(False)
        else:
            self.water.setEnabled(True)
            self.internet.setEnabled(True)
            self.sewage.setEnabled(True)

Answer 1

One solution is to calculate the opposite, that is, if the number of unchecked buttons is 1 and then disable it or not:

class MyApp(QtWidgets.QMainWindow, Ui_MainWindow):
    def __init__(self):
        QtWidgets.QMainWindow.__init__(self)
        self.setFixedSize(250, 330)
        self.setupUi(self)

        self.sewage.stateChanged.connect(self.onStateChange)
        self.water.stateChanged.connect(self.onStateChange)
        self.internet.stateChanged.connect(self.onStateChange)

    @pyqtSlot()
    def onStateChange(self):
        buttons = [self.water, self.sewage, self.internet]
        uncheckeds = [btn for btn in buttons if not btn.isChecked()]
        for btn in uncheckeds:
            btn.setDisabled(len(uncheckeds) == 1)

The same logic can be done with QButtonGroup:

class MyApp(QtWidgets.QMainWindow, Ui_MainWindow):
    def __init__(self):
        QtWidgets.QMainWindow.__init__(self)
        self.setFixedSize(250, 330)
        self.setupUi(self)

        self.m_group = QtWidgets.QButtonGroup(
            self, exclusive=False, buttonClicked=self.onButtonClicked
        )
        for btn in (self.sewage, self.water, self.internet):
            self.m_group.addButton(btn)

    @QtCore.pyqtSlot()
    def onButtonClicked(self):
        uncheckeds = [
            btn for btn in self.m_group.buttons() if not btn.isChecked()
        ]
        for btn in uncheckeds:
            btn.setDisabled(len(uncheckeds) == 1)