PyQt class inheritance

Question

I am having troubles to understand class inheritance with Python/PyQt. I have a MainWindow and a Popup QWidget. I want to interact with the self.label1 of the MainWindow after the QWidget was opened in a pop up window but I don't know how to do it. I know only the other way around, to reach all widgets from the popup Window inside MainWindow but not vice versa.

Here is an example, self.label1 of MainWindow should get another text after MyPopup opens in a new window:

import sys
from PyQt4.Qt import *

class MyPopup(QWidget):
    def __init__(self):
        QWidget.__init__(self)

        # I want to change the lable1 of MainWindow
        self.cw.label1.setText('hello')


class MainWindow(QMainWindow):
    def __init__(self, *args):
        QMainWindow.__init__(self, *args)
        self.cw = QWidget(self)
        self.setCentralWidget(self.cw)
        self.btn1 = QPushButton("Click me", self.cw)
        self.btn1.setGeometry(QRect(50, 50, 100, 30))
        self.label1 = QLabel("No Commands running", self.cw)
        self.connect(self.btn1, SIGNAL("clicked()"), self.doit)
        self.w = None

    def doit(self):
        self.w = MyPopup()
        self.w.setGeometry(QRect(100, 100, 400, 200))
        self.w.show()

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

Answer 1

You need to pass the main window as a parameter to the constructor of MyPopup, try this:

import sys
from PyQt4.Qt import *

class MyPopup(QWidget):
    def __init__(self, mainWindow):
        QWidget.__init__(self)

        # use the mainWindow passed as parameter
        mainWindow.label1.setText('hello')


class MainWindow(QMainWindow):
    def __init__(self, *args):
        QMainWindow.__init__(self, *args)
        self.cw = QWidget(self)
        self.setCentralWidget(self.cw)
        self.btn1 = QPushButton("Click me", self.cw)
        self.btn1.setGeometry(QRect(50, 50, 100, 30))
        self.label1 = QLabel("No Commands running", self.cw)
        self.connect(self.btn1, SIGNAL("clicked()"), self.doit)
        self.w = None

    def doit(self):
        self.w = MyPopup(self) #when creating the popup pass in the main window
        self.w.setGeometry(QRect(100, 100, 400, 200))
        self.w.show()

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