helloworld.py

# helloworld.py
import pathlib
import pygubu

PROJECT_PATH = pathlib.Path(__file__).parent
PROJECT_UI = PROJECT_PATH / "helloworld.ui"


class HelloworldApp:
    def __init__(self, master=None):
        # 1: Create a builder and setup resources path (if you have images)
        self.builder = builder = pygubu.Builder()
        builder.add_resource_path(PROJECT_PATH)

        # 2: Load an ui file
        builder.add_from_file(PROJECT_UI)

        # 3: Create the mainwindow
        self.mainwindow = builder.get_object("mainwindow", master)

        # 4: Connect callbacks
        builder.connect_callbacks(self)

    def run(self):
        self.mainwindow.mainloop()


if __name__ == "__main__":
    app = HelloworldApp()
    app.run()