当QProgressBar存在时如何居中对齐QPushButton？

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

class MyWidget(QWidget):
    def __init__(self):
        super().__init__()
        self.initUI()

    def initUI(self):
        progressBar = QProgressBar(self)
        button = QPushButton("Button", self)

        layout = QHBoxLayout()
        layout.addWidget(progressBar)
        layout.addWidget(button)
        layout.setAlignment(progressBar, Qt.AlignCenter)
        layout.setAlignment(button, Qt.AlignCenter)

        self.setLayout(layout)

if __name__ == '__main__':
    app = QApplication(sys.argv)
    widget = MyWidget()
    widget.show()
    sys.exit(app.exec_())