Qt Designer and Python run a function in separate functions.py

Question

I'm new to python. I designed a GUI in QtDesigner and translated the code to use it with python. Since if I change something in the GUI it will overwrite my code I want to use a separate file for the functions.

The code should run after the main window is shown but I get an error

Ui_MainWindow' object has no attribute 'fillContactList'

I would really appreciate if anyone would help me.

import sys
import psycopg2
from PySide6 import (QtCore, QtWidgets, QtGui)
from PySide6.QtCore import (QCoreApplication, QDate, QDateTime, QLocale,
     QMetaObject, QObject, QPoint, QRect,
     QSize, QTime, QUrl, Qt)
from PySide6.QtGui import (QBrush, QColor, QConicalGradient, QCursor,
    QFont, QFontDatabase, QGradient, QIcon,
    QImage, QKeySequence, QLinearGradient, QPainter,
    QPalette, QPixmap, QRadialGradient, QTransform)
from PySide6.QtWidgets import (QApplication, QLabel, QMainWindow, QMenuBar,
    QSizePolicy, QStatusBar, QTabWidget, QWidget)

from mainwindow import Ui_MainWindow

class mainwindow(QMainWindow, Ui_MainWindow):

   def __init__(self):
       super(mainwindow, self).__init__()
       self.setWindowTitle("Skills In Motion")

   def fillContactList(self):
           conn = psycopg2.connect(database="CRM", user="********", password="*****", host="localhost", port=5432)
           cur = conn.cursor()
           dataset = cur.execute("SELECT cust_name, cust_pk FROM customer")
           results = cur.fetchall()
           
           rowPosition = 0
           for customers in results:
               self.contactsTable.insertRow(rowPosition)
               self.contactsTable.setItem(rowPosition,0,QtWidgets.QTableWidgetItem(customers[0]))
               self.contactsTable.setItem(rowPosition,1,QtWidgets.QTableWidgetItem(str(customers[1])))
               self.contactsTable.hideColumn(1)
               rowPosition = rowPosition+1
           self.contactsTable.itemSelectionChanged.connect(self.onSelectionContact)
           self.contactsTable.selectRow(0)

   if __name__ == "__main__":
       import sys
       app = QtWidgets.QApplication(sys.argv)
       MainWindow = QtWidgets.QMainWindow()
       ui = Ui_MainWindow()
       ui.setupUi(MainWindow)
       ui.fillContactList()
       MainWindow.show()
       sys.exit(app.exec())```

Answer 1

First, You should rename mainwindow class to MainWindow. MainWindow need to be subclassed from QMainWindow only.

After creating Ui_MainWindow object, use its setupUi method to build your MainWindow object. All the widgets reference that you created in designer will be available as attributes of Ui_MainWindow object.

So, store it in main window as self.ui = Ui_MainWindow(). Build main window as self.ui.setupUi(self). Reference any widgets like self.ui.contactsTable

You need to create object of your MainWindow class, not QMainWindow

Try like this:

import sys
from PySide6.QtWidgets import QMainWindow, QApplication
from mainwindow import Ui_MainWindow


class MainWindow(QMainWindow):

    def __init__(self):
        super().__init__()
        self.setWindowTitle("Skills In Motion")
        self.ui = Ui_MainWindow()
        self.ui.setupUi(self)
        self.fillContactList()

    def fillContactList(self):
        # Reference Table like this
        # self.ui.contactsTable
        pass


if __name__ == '__main__':
    app = QApplication(sys.argv)
    mainWindow = MainWindow()
    mainWindow.show()
    sys.exit(app.exec_())