Untitled

#  -*- coding: utf-8 -*-


from PyQt4 import QtCore, QtGui
import ui_Calc


def calc():

    try:
        res = self.first - self.second
    except:
        res = "?"
    MainWindow.result.setText(QString (res));


class MyWindow(QtGui.QWidget, ui_Calc.Ui_MainWindow):


    def __init__(self , parent = None):
        QtGui.QWidget.__init__(self, parent)
        self.setupUi(self)
        self.connect(self.exit, QtCore.SIGNAL("clicked()"), self.close)
        self.connect(self.calculate,QtCore.SIGNAL("clicked()"),calc)

if __name__ == "__main__":
    import sys
    app = QtGui.QApplication(sys.argv)
    window = MyWindow()
    window.show()
    sys.exit(app.exec_())