add a layout to another layout from the parent window

Question

I am new to this field, and I Hope this not seems a stupid question I am using PyQt5 for Python 3.8 on mac I want to add a layout(addLayout) to another layout from the parent window if it is possible!

This is an example: I have a Class (ParentWindow) it has many widgets and hboxlayout. (ChildWindow) is a class inherited from ParentWindow and it has also widgets and other layout; the question: can I add layout in the child window? If I use setLayout in the ChildWindow it ignores it and show the message: (QWidget::setLayout: Attempting to set QLayout "" on ChildWindow "", which already has a layout) So, can I use addLayout to the parent window layout? And how

# The Parent Class
from PyQt5.QtWidgets import  QWidget, QHBoxLayout,QLabel
class ParentWindow(QWidget):
    def __init__(self):
        super().__init__()
        title = "Main Window"
        self.setWindowTitle(title)
        left = 000; top = 500; width = 600; hight = 300
        self.setGeometry(left, top, width, hight)
        MainLayoutHbox = QHBoxLayout()
        header1 = QLabel("Header 1")
        header2 = QLabel("Header 2")
        header3 = QLabel("Header 3")
        MainLayoutHbox.addWidget(header1)
        MainLayoutHbox.addWidget(header2)
        MainLayoutHbox.addWidget(header3)
        self.setLayout(MainLayoutHbox)
# End of Parent Class


# The SubClass

from PyQt5.QtWidgets import QApplication,   QVBoxLayout, QHBoxLayout,  QTabWidget, QLabel
import sys

from ParentWindow import ParentWindow


class ChildWindow(ParentWindow):
    def __init__(self):
        super().__init__()
        vbox = QVBoxLayout()
        MainLabel= QLabel("My Window")

        vbox.addWidget(MainLabel)

        self.setLayout(vbox) # This show the Warning  Error

        # I assume the below code should work to extend the parent layout!! But it gives error
        # parent.MainLayoutHbox.addLayout(vbox)




if __name__ == "__main__":
    App = QApplication(sys.argv)
    MyWindow= ChildWindow()
    MyWindow.show()
    App.exec()

Answer 1

ChildWindow is a ParentWindow, that is, ChildWindow has the preset properties in ParentWindow that where you added a layout and with your Z code you are adding a layout but Qt tells you: QWidget::setLayout: Attempting to set QLayout "" on ChildWindow "", which already has a layout which indicates that you already have a layout (the layout that you inherited from the parent ).

If you want to add MainLabel to the pre-existing layout through another layout then you must access the inherited layout using the "layout()" method and add it:

class ChildWindow(ParentWindow):
    def __init__(self):
        super().__init__()
        vbox = QVBoxLayout()
        MainLabel= QLabel("My Window")
        vbox.addWidget(MainLabel)
        # self.layout() is MainLayoutHbox
        self.layout().addLayout(vbox)