在窗口标题栏的左上方显示图标

效果如下图：

"""
This example shows an icon
in the titlebar of the window.

"""

import sys
from PyQt5.QtWidgets import QApplication, QWidget
from PyQt5.QtGui import QIcon


class Example(QWidget):  # The Example class inherits from the QWidget class

    def __init__(self):
        super().__init__()  # The super() method returns the parent object of the Example class

        self.initUI()

    def initUI(self):

        # locates the window on the screen and sets it size
        self.setGeometry(300, 300, 300, 220)

        # set the title of the window
        self.setWindowTitle('Hello World')

        # sets the application icon
        # The QIcon receives the path to our icon
        self.setWindowIcon(QIcon('web.png'))

        self.show()


if __name__ == '__main__':

    app = QApplication(sys.argv)
    ex = Example()
    sys.exit(app.exec_())

问题：如何将标题居中？