Mr.

#callMDI.pyw
import sys

from MDI1 import *

class MyForm(QtGui.QMainWindow):
    def __init__(self, parent=None):
        QtGui.QWidget.__init__(self, parent)
        self.ui = Ui_MainWindow()
        self.ui.setupUi(self)
        self.ui.mdiArea.addSubWindow(self.ui.subwindow)
        self.ui.mdiArea.addSubWindow(self.ui.subwindow_2)
        QtCore.QObject.connect(self.ui.showNext, QtCore.SIGNAL('clicked()'),self.displayNext)
        QtCore.QObject.connect(self.ui.showPrevious, QtCore.SIGNAL('clicked()'),self.displayPrevious)
        QtCore.QObject.connect(self.ui.closeAll, QtCore.SIGNAL('clicked()'),self.closeAll)
        QtCore.QObject.connect(self.ui.cascadeButton, QtCore.SIGNAL('clicked()'),self.cascadeArrange)
        QtCore.QObject.connect(self.ui.tileButton, QtCore.SIGNAL('clicked()' ),self.tileArrange)
        QtCore.QObject.connect(self.ui.SubWindowViewButton,
        QtCore.SIGNAL('clicked()'), self.SubWindowView)
        QtCore.QObject.connect(self.ui.TabbedViewButton, QtCore.SIGNAL('clicked()'),self.TabbedView)
        self.connect(self.ui.actionFirst_Window, QtCore.SIGNAL('triggered()' ),self.displayNext)
        self.connect(self.ui.actionSecond_Window, QtCore.SIGNAL('triggered()'),self.displayPrevious)

    def displayNext(self):
        self.ui.mdiArea.activateNextSubWindow()
    def displayPrevious(self):
        self.ui.mdiArea.activatePreviousSubWindow()
    def closeAll(self):
        self.ui.mdiArea.closeAllSubWindows()
    def cascadeArrange(self):
        self.ui.mdiArea.cascadeSubWindows()
    def tileArrange(self):
        self.ui.mdiArea.tileSubWindows()
    def SubWindowView(self):
        self.ui.mdiArea.setViewMode(0)
    def TabbedView(self):
        self.ui.mdiArea.setViewMode(1)

if __name__ == "__main__":
    app = QtGui.QApplication(sys.argv)
    myapp = MyForm()
    myapp.show()
    sys.exit(app.exec_())