def on_inputSpinBox1_valueChanged(self, value):
    self.ui.outputWidget.setText(QtCore.QString.number(value + self.ui.
        inputSpinBox2.value()))

@QtCore.pyqtSignature('int')
def on_inputSpinBox2_valueChanged(self, value):
    self.ui.outputWidget.setText(QtCore.QString.number(value + self.ui.
        inputSpinBox1.value()))
if __name__ == '__main__':
    app = QtGui.QApplication(sys.argv)
calculator = CalculatorForm()
calculator.show()
sys.exit(app.exec_())
Loading a simple Qt Designer form in to Pyside