Friendpaste

import sys
from PySide import QtCore, QtGui

class Test(QtGui.QMainWindow):
    def __init__(self):
        QtGui.QMainWindow.__init__(self)

        self.button = QtGui.QPushButton(self)
        self.button.setText(QtCore.QString("Push me"))  
        self.setCentralWidget(self.button)

        self.secondWindow = QtGui.QMainWindow(self)
        self.secondWindow.setParent(self)

        self.connect(self.button, QtCore.SIGNAL("clicked()"), self.openSecondWindow)

    def openSecondWindow(self):
        print "Activate second window"
        self.secondWindow.show()

if __name__ == '__main__':
    app = QtGui.QApplication(sys.argv)
    test = Test()
    test.show()
    sys.exit(app.exec_())