pyqt/basic/layout_7.py

import sys

from PyQt5.QtWidgets import QMainWindow, QStackedLayout, QWidget, QApplication

from layout_colorwidget import Color


class MainWindow(QMainWindow):
    def __init__(self):
        super().__init__()
        self.setWindowTitle("My App")

        layout = QStackedLayout()

        layout.addWidget(Color("red"))
        layout.addWidget(Color("gree"))
        layout.addWidget(Color("blue"))
        layout.addWidget(Color("purple"))
        layout.addWidget(Color("yellow"))

        layout.setCurrentIndex(4)

        widget = QWidget()
        widget.setLayout(layout)
        self.setCentralWidget(widget)


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