https://stackoverflow.com/questions/50430093/how-to-avoid-double-inhertince

main.py

from PyQt5.QtWidgets import *
from PyQt5.QtGui import *
from PyQt5.QtCore import *

class Manager:
	def __init__(self):
		self.center()

	def center(self):
		self.setGeometry(QStyle.alignedRect(
			Qt.LeftToRight,
			Qt.AlignCenter,
			self.size(),
			QApplication.desktop().availableGeometry()
			)
		)

	def setBackgroundColor(self, color):
		pal = self.palette()
		pal.setColor(QPalette.Background, color)
		self.setPalette(pal)

class MainWindow(QMainWindow, Manager):
	def __init__(self):
		QMainWindow.__init__(self)
		Manager.__init__(self)
		self.setBackgroundColor(QColor("pink"))

if __name__ == '__main__':
	import sys

	app = QApplication(sys.argv)
	w = MainWindow()
	w.show()
	sys.exit(app.exec_())