Python-сообщество

from PyQt4 import QtGui, QtCore
import sys
from main import Ui_Form_main
from secondary import Ui_Form_secondary


class Main(QtGui.QMainWindow):
    def __init__(self, parent=None):
        QtGui.QWidget.__init__(self, parent)
        self.ui = Ui_Form_main()
        self.ui.setupUi(self)

class Secondary(QtGui.QMainWindow):
    def __init__(self, parent=None):
        QtGui.QWidget.__init__(self, parent)
        self.ui = Ui_Form_secondary()
        self.ui.setupUi(mainObj)
        
    
app = QtGui.QApplication(sys.argv)

mainObj = Main()
mainObj.show()

secondObj = Secondary(mainObj)
secondObj.show()

app.exec_()

self.ui.setupUi(mainObj)