How can I get rid of the previous layout and set new Grid Layout in QMainWindow?

Question

I am a newbie with PyQt. I am trying to organize my buttons on a grid layout, but I guess the window has a default layout already. How can I get rid of it and replace it with the new Grid Layout? I have contained the code block relevant with hashes ###, Here is my program:

import sys
from PyQt4 import QtCore, QtGui
from PyQt4.QtGui import QWidget

class MainWindow(QtGui.QMainWindow):
    def __init__(self):
        QtGui.QWidget.__init__(self)

        self.setMinimumSize (800,600) # set minimum size for window
        self.setWindowTitle("CoolPlay Kabul") # set window title

        self.setWindowIcon(QtGui.QIcon("images/CoolPlay.png"))# set icon for Window


        myMenu = self.menuBar()
        File_Menu = myMenu.addMenu("&File")
        Items_Menu = myMenu.addMenu("&Items")
        Playlist_Menu = myMenu.addMenu("&Playlist")
        Option_Menu = myMenu.addMenu("&Option")
        Exit_Menu = myMenu.addMenu("&Exit")

        File_Menu.addAction("New Time")
        File_Menu.addAction("Delete Time")
        File_Menu.addSeparator()
        File_Menu.addAction("Exit")

        Items_Menu.addAction("New Item")
        Items_Menu.addAction("Delete Item")
        Items_Menu.addSeparator()
        Items_Menu.addAction("Toggle Segue")

        Playlist_Menu.addAction("Clear Playlist")
        Playlist_Menu.addAction("Save playlist")
        Playlist_Menu.addAction("Load Playlist")
        Playlist_Menu.addSeparator()
        Playlist_Menu.addAction("Clear 'Played' Indication")

        Option_Menu.addAction("Application Setup")

        Exit_Menu.addAction("Help")
        Exit_Menu.addAction("About")

        ######################################################
        Overall_Layout = QtGui.QGridLayout(self)
        self.setLayout(Overall_Layout)

        Play_Button = QtGui.QPushButton(QtGui.QIcon("images/PLAY.bmp"), "PLAY",self)
        Overall_Layout.addWidget(Play_Button,1,2)
        Overall_Layout.addWidget(Play_Button,2,2)

        ########################################################


        self.show()
if __name__ == "__main__":

    app = QtGui.QApplication(sys.argv)
    CoolPlay = MainWindow()


    CoolPlay.show()
    sys.exit(app.exec_())

Answer 1

QMainWindow is a special widget since it already has a preset layout as shown below:

So in this case you should not set a layout to the QMainWindow but to the central widget, but first establish a centralwidget, using the indicated thing we get the following:

######################################################
central_widget = QtGui.QWidget()
self.setCentralWidget(central_widget)
Overall_Layout = QtGui.QGridLayout(central_widget)
Play_Button = QtGui.QPushButton(QtGui.QIcon("images/PLAY.bmp"), "PLAY")
Overall_Layout.addWidget(Play_Button,1,2)
Overall_Layout.addWidget(Play_Button,2,2)

########################################################

On the other hand if you inherit from QMainWindow you must call the QMainWindow constructor, but in code you call QWidget, so you must modify it to:

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

Or

class MainWindow(QtGui.QMainWindow):
    def __init__(self):
        super(MainWindow, self).__init__()