Center Child QMainWindow Relative to Parent QMainWindow

Question

The area of focus is on this part of the code:

prect = self.parent.rect() # <===
prect1 = self.parent.geometry() # <===
center = prect1.center() # <===
self.move(center) # <===

When I use prect.center(), it centers the box correctly in the center, but if I move the window and use the menu (Action > Show Window2), Window2 doesn't show centered relative to the parent window.

When I use prect1.center(), it doesn't center the box correctly (top-left coordinate of Window2 is in the center) but it does move relative to the parent window if I move the parent window somewhere else.

Question: How do I alter my code to show Window2 in the center of Window relative to wherever Window is at on the screen?

Reproducible code example:

import sys
from PyQt5 import QtGui
from PyQt5.QtWidgets import (QApplication, QMainWindow, QAction)

class Window(QMainWindow):
    def __init__(self):
        super().__init__()

        self.top = 100
        self.left = 100
        self.width = 680
        self.height = 500
        self.setWindowTitle("Main Window")
        self.setGeometry(self.top, self.left, self.width, self.height)

        menu = self.menuBar()
        action = menu.addMenu("&Action")
        show_window2 = QAction("Show Window2", self)
        action.addAction(show_window2)
        show_window2.triggered.connect(self.show_window2_centered)

        self.show()

    def show_window2_centered(self):                                             
        self.w = Window2(parent=self)
        self.w.show()

class Window2(QMainWindow):
    def __init__(self, parent=None):
        self.parent = parent
        super().__init__()
        self.setWindowTitle("Centered Window")

        prect = self.parent.rect() # <===
        prect1 = self.parent.geometry() # <===
        center = prect1.center() # <===
        self.move(center) # <===
        print(prect)
        print(prect1)
        print(center)

if __name__ == "__main__":
    app = QApplication(sys.argv)
    window = Window()
    sys.exit(app.exec())

Currently looks like this:

Would like it to be centered relative to the main window:

Answer 1

First self.w is not a child ofWindow because you do not pass that parameter to super(). On the other hand move() does not center the widget in that position, what it does is that the top-left is located in that position.

The solution is to modify the geometry using the geometry of the other element since they are both windows:

class Window2(QMainWindow):
    def __init__(self, parent=None):
        self.parent = parent
        super().__init__()
        self.setWindowTitle("Centered Window")

        geo = self.geometry()
        geo.moveCenter(self.parent.geometry().center())
        self.setGeometry(geo)