pyqt/designer/example_1.py

import os.path
import sys

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

basedir = os.path.dirname(__file__)

app = QApplication(sys.argv)

window = uic.loadUi(os.path.join(basedir, "mainwindow.ui"))
window.show()

app.exec_()