Pupli

import sys
import os

from PySide2.QtWidgets import QApplication, QWidget, QPushButton
from PySide2.QtCore import QFile
from PySide2.QtUiTools import QUiLoader


class main(QWidget):
    def __init__(self):
        super(main, self).__init__()
        self.load_ui()

    def load_ui(self):
        loader = QUiLoader()
        path = os.path.join(os.path.dirname(__file__), "form.ui")
        ui_file = QFile(path)
        ui_file.open(QFile.ReadOnly)
        self.window:QWidget = loader.load(ui_file, self)
        ui_file.close()

        # pushButton is the name of button control
        self.pushButton:QPushButton = self.window.findChild(QPushButton,"pushButton")
        self.pushButton.clicked.connect(self.clicked)

    def clicked(self):
        print("Hello")


if __name__ == "__main__":
    app = QApplication([])
    widget = main()
    widget.show()
    sys.exit(app.exec_())

References
https://www.blog.pythonlibrary.org/2018/05/30/loading-ui-files-in-qt-for-python/

import sys
import os


from PySide2.QtWidgets import QApplication, QWidget
from PySide2.QtCore import QFile
from PySide2.QtUiTools import QUiLoader


class main(QWidget):
    def __init__(self):
        super(main, self).__init__()
        self.load_ui()

    def load_ui(self):
        loader = QUiLoader()
        path = os.path.join(os.path.dirname(__file__), "form.ui")
        ui_file = QFile(path)
        ui_file.open(QFile.ReadOnly)
        loader.load(ui_file, self)
        ui_file.close()

if __name__ == "__main__":
    app = QApplication([])
    widget = main()
    widget.show()
    sys.exit(app.exec_())