Implementing widgets within a main window

I am learning PySide and am trying to implement widgets within a main window. My goal right now is very simple: I want to place a QLabel, with independently defined event handling, inside a main window that has its own event handling:

# -*- coding: utf-8 -*-
from PySide import QtGui, QtCore

class MainWindow(QtGui.QWidget):
    '''Main window lets user know when window was clicked on non-widget space'''
    def __init__(self):
        QtGui.QWidget.__init__(self)
        self.initUI()    
    def initUI(self):
        self.myLabel=TalkingQLabel("Don't mess with Breakfast!", self) 
        self.myLabel.setGeometry(50, 50, 200, 120)       
        self.setGeometry(300,200,300,250)
        self.show()
    def mousePressEvent(self, event):
        print "Well, you pressed in main window!"

class TalkingQLabel(QtGui.QLabel):
    '''QLab el that indicates when it was pressed'''
    def __init__(self, txt, parent):
        QtGui.QLabel.__init__(self, txt, parent)
        self.initUI()
    def initUI(self):
        self.setAlignment(QtCore.Qt.AlignCenter)
        self.setStyleSheet("QLabel { color: rgb(255, 255, 0); font-size: 15px; background-color: rgb(0,0,0)}")
    def mousePressEvent(self, event):
        print "This time you pressed in a label"                

def main():
    import sys
    qtApp=QtGui.QApplication(sys.argv)
    myTalker=MainWindow()
    sys.exit(qtApp.exec_())

if __name__=="__main__":
    main()

Was it good practice to have two separate classes like this for Qt programming, or should I have defined TalkingQLabel within MainWindow because they are in a parent-child relationship, and always will be in this application? Is there a standard within the Qt community I should know about, especially in cases when one widget is a child of another?

Related pages:

• https://stackoverflow.com/questions/330/should-i-use-nested-classes-in-this-case
• Nested class or two separate classes?
• https://stackoverflow.com/questions/1581931/should-i-refactor-static-nested-classes-in-java-into-separate-classes
• https://softwareengineering.stackexchange.com/questions/171790/are-nested-classes-under-rated