pyqt/load_uifile.py

import sys

from PyQt5 import QtWidgets, uic
from PyQt5.QtWidgets import QMainWindow

from MainWindow import Ui_MainWindow


class MainWindow(QMainWindow, Ui_MainWindow):
    def __init__(self, *args, **kwargs):
        super(MainWindow, self).__init__(*args, **kwargs)
        self.setupUi(self)


def mainwindow_setup(w):
    w.setTitle("MainWindow Title")


if __name__ == '__main__':
    app = QtWidgets.QApplication(sys.argv)

    # window = uic.loadUi("mainwindow.ui")
    # mainwindow_setup(window)
    window = MainWindow()
    window.show()
    app.exec()