TI/PyQt5

import sys
from PyQt5.QtWidgets import QApplication, QWidget, QPushButton

class App(QWidget):

    def __init__(self):
        super().__init__()
        self.title = 'Guzik'
        self.left = 10
        self.top = 10
        self.width = 220
        self.height = 220
        self.initUI()
    
    def initUI(self):
        self.setWindowTitle(self.title)
        self.setGeometry(self.left, self.top, self.width, self.height)
        
        self.guzik= QPushButton('X', self)
        self.guzik.move(10,10)
        self.guzik.resize(200,200)
        self.guzik.clicked.connect(self.on_click)
        self.show()

    def on_click(self):
        if self.guzik.text()=='X':
            self.guzik.setText('O')
        else:
            self.guzik.setText('X')

if __name__ == '__main__':
    app = QApplication(sys.argv)
    ex = App()
    sys.exit(app.exec_())