import sys
from PyQt5.QtWidgets import QApplication, QWidget, QDesktopWidget
class Example(QWidget):
    def __init__(self):
        super().__init__()
        self.initUI()


    def initUI(self):
        self.resize(250, 150)
        self.center()
        self.setWindowTitle('視窗定在螢幕中心')
        self.show()
    def center(self):
        qr = self.frameGeometry()
        cp = QDesktopWidget().availableGeometry().center()
        qr.moveCenter(cp)
        self.move(qr.topLeft())

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