python how to amend file after importing

Question

I've just realized only after having lost all the changes I made, that once you go back to the QT designer and amend something on the GUI and convert that back to a .py file all changes are erased on the previous .py file.

Would you recommend that I save it to a new .py file then copy & paste or is there a better 'professional' way to do this?

EDIT:

I have now managed to import the file instead of amending it with the code below:

from PyQt4 import QtCore, QtGui
from mysqlviewer import Ui_MainWindow

class MainWindow(QtGui.QMainWindow, Ui_MainWindow):

    def __init__(self, parent=None):
        super(MainWindow, self).__init__(parent)
        self.setupUi(self)



if __name__ == "__main__":
    import sys
    app = QtGui.QApplication(sys.argv)
    MainWindow = QtGui.QMainWindow()
    ui = Ui_MainWindow()
    ui.setupUi(MainWindow)
    MainWindow.show()
    sys.exit(app.exec_())

I am now trying to simply add an item to the comboBox of the UI but it does not show.

Here is what I am attempting,

from PyQt4 import QtCore, QtGui
from mysqlviewer import Ui_MainWindow

class MainWindow(QtGui.QMainWindow, Ui_MainWindow):

    def __init__(self, parent=None):
        super(MainWindow, self).__init__(parent)
        self.setupUi(self)

        self.comboBox_2.addItem("Example Item")

if __name__ == "__main__":
    import sys
    app = QtGui.QApplication(sys.argv)
    MainWindow = QtGui.QMainWindow()
    ui = Ui_MainWindow()
    ui.setupUi(MainWindow)
    MainWindow.show()
    sys.exit(app.exec_())

Answer 1

Don't modify your auto-generated file. Just import and inherit from it:

from PySide import QtCore, QtGui
# modify the import if needed
# from PyQt5 import QtCore, QtGui
# from PyQt4 import QtCore, QtGui

from ui import Ui_MainWindow

class MainWindow(QtGui.QMainWindow, Ui_MainWindow):
    """Main Window.
    """
    def __init__(self, parent=None):
        super(MainWindow, self).__init__(parent)
        self.setupUi(self)
        #  your code here

Here ui is the auto-generated module. No code changes are needed next time you update it.

Answer 2

I have found that the best way to import & use the file is as follows, this may just be in addition to the other answer.

import sys
from PyQt4 import QtCore, QtGui
from mysqlviewer import*

class Window(QtGui.QMainWindow):

     def __init__(self, parent=None):
        QtGui.QWidget.__init__(self, parent)
        self.ui = Ui_MainWindow()
        self.ui.setupUi(self)


        self.ui.comboBox.addItem("Example Item")

if __name__ == "__main__":

    app = QtGui.QApplication(sys.argv)
    viewer = Window()
    viewer.show()
    sys.exit(app.exec_())