加载PyQt5 UI文件时出错

我正在使用以下代码加载ui文件,但始终看到错误消息。

# main.py
import sys
from PyQt5.QtWidgets import *
from PyQt5 import uic

form_class = uic.loadUiType("main_window.ui")[0]

class MyWindow(QMainWindow, form_class):
    def __init__(self):
        super().__init__()
        self.setupUi(self)

if __name__ == "__main__":
    app = QApplication(sys.argv)
    myWindow = MyWindow()
    myWindow.show()
    app.exec_()

Error message:
    FileNotFoundError: [Errno 2] No such file or directory: 'main_window.ui'

main_window.ui 与位于同一文件夹中 main.py