title: how to call another window in pyqt4 python?
body: <p>how to call another window in pytq4?
  For example i have two separate form. I want to show the second form when i click a button in the login form.</p>
  
  <p>EDITED:
  for example i have this dialog for my login.
  when the user click a button the main.py would appear and this dialog will be close.</p>
  
  <p>LOGIN.py
      from PyQt4 import QtCore, QtGui</p>
  
  <pre><code>class Ui_Dialog(object):
      def setupUi(self, Dialog):
          Dialog.setObjectName("Dialog")
          Dialog.resize(379, 184)
          self.buttonBox = QtGui.QDialogButtonBox(Dialog)
          self.buttonBox.setGeometry(QtCore.QRect(20, 130, 341, 32))
          self.buttonBox.setOrientation(QtCore.Qt.Horizontal)
          self.buttonBox.setStandardButtons(QtGui.QDialogButtonBox.Cancel|QtGui.QDialogButtonBox.Ok)
          self.buttonBox.setObjectName("buttonBox")
  
          self.retranslateUi(Dialog)
          QtCore.QObject.connect(self.buttonBox, QtCore.SIGNAL("accepted()"), Dialog.accept)
          QtCore.QObject.connect(self.buttonBox, QtCore.SIGNAL("rejected()"), Dialog.reject)
          QtCore.QMetaObject.connectSlotsByName(Dialog)
  
      def retranslateUi(self, Dialog):
          Dialog.setWindowTitle(QtGui.QApplication.translate("Dialog", "Dialog", None, QtGui.QApplication.UnicodeUTF8))
  
  
  if __name__ == "__main__":
      import sys
      app = QtGui.QApplication(sys.argv)
      Dialog = QtGui.QDialog()
      ui = Ui_Dialog()
      ui.setupUi(Dialog)
      Dialog.show()
      sys.exit(app.exec_())
  </code></pre>
  
  <p>MAIN.py</p>
  
  <pre><code>from PyQt4 import QtCore, QtGui
  
  class Ui_MainWindow(object):
      def setupUi(self, MainWindow):
          MainWindow.setObjectName("MainWindow")
          MainWindow.resize(595, 315)
          self.centralwidget = QtGui.QWidget(MainWindow)
          self.centralwidget.setObjectName("centralwidget")
          MainWindow.setCentralWidget(self.centralwidget)
  
          self.retranslateUi(MainWindow)
          QtCore.QMetaObject.connectSlotsByName(MainWindow)
  
      def retranslateUi(self, MainWindow):
          MainWindow.setWindowTitle(QtGui.QApplication.translate("MainWindow", "MainWindow", None, QtGui.QApplication.UnicodeUTF8))
  </code></pre>