pyqt/basic/layout_8.py

import sys

from PyQt5.QtWidgets import QMainWindow, QStackedLayout, QWidget, QApplication, QVBoxLayout, QHBoxLayout, QPushButton

from layout_colorwidget import Color


class MainWindow(QMainWindow):

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

        page_layout = QVBoxLayout()
        button_layout = QHBoxLayout()
        self.stack_layout = QStackedLayout()

        page_layout.addLayout(self.stack_layout)
        page_layout.addLayout(button_layout)

        btn = QPushButton("red")
        btn.pressed.connect(self.activate_tab_1)
        button_layout.addWidget(btn)
        self.stack_layout.addWidget(Color("red"))

        btn = QPushButton("green")
        btn.pressed.connect(self.activate_tab_2)
        button_layout.addWidget(btn)
        self.stack_layout.addWidget(Color("green"))

        btn = QPushButton("yellow")
        btn.pressed.connect(self.activate_tab_3)
        button_layout.addWidget(btn)
        self.stack_layout.addWidget(Color("yellow"))

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

    def activate_tab_1(self):
        self.stack_layout.setCurrentIndex(0)

    def activate_tab_2(self):
        self.stack_layout.setCurrentIndex(1)

    def activate_tab_3(self):
        self.stack_layout.setCurrentIndex(2)


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