pyqt/basic/signals_and_slots_1c.py

import sys

from PyQt5.QtWidgets import QMainWindow, QPushButton, QApplication


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

        self.button_is_checked = True

        self.setWindowTitle("My App")

        button = QPushButton("Press Me!")
        button.setCheckable(True)
        button.clicked.connect(self.the_button_was_toggled)
        button.setChecked(self.button_is_checked)

        # Set the central widget of the window
        self.setCentralWidget(button)

    def the_button_was_toggled(self, is_checked):
        self.button_is_checked = is_checked

        print(self.button_is_checked)


app = QApplication(sys.argv)

window = MainWindow()
window.show()

app.exec_()