python - Access A Variable from another class in PyQt5

Question

In PyQt5, I've wrote a GUI. Basically, when a button is pressed, it open a new window, where choose an item from a list. What I want is that after you close the new window, the item you chose appears as text on the first window. It's a bit hard to explain.

This is the code:

import sys
from PyQt5.QtCore import Qt
from PyQt5.QtGui import QFont
from PyQt5 import QtWidgets
from PyQt5 import QtCore 
from PyQt5 import QtGui

class Add(QtWidgets.QMainWindow):
    def __init__(self):
        super(Add, self).__init__()

        #Set The UI
        self.initUI()
        #Set The GUI Position And Size
        self.setGeometry(1050, 500, 400, 50)
        #Set The GUI Title
        self.setWindowTitle("Add")
        
    def initUI(self):
        Central = QtWidgets.QWidget(self)
        self.setCentralWidget(Central)

        self.deckButton = QtWidgets.QPushButton(self)
        self.deckButton.setText("Choose")
        self.deckButton.clicked.connect(self.open_deck_browser)

        hbox = QtWidgets.QHBoxLayout()
        hbox.addWidget(self.deckButton, 1)

        Central.setLayout(hbox)

    def open_deck_browser(self):
        self.w = SetDeck()
        self.w.show()

class SetDeck(QtWidgets.QMainWindow):
    def __init__(self):
        super(SetDeck, self).__init__()

        #Set The UI
        self.initUI()
        #Set The GUI Position And Size
        self.setGeometry(200, 200, 800, 640)
        #Set The GUI Title
        self.setWindowTitle("Choose Deck")
        
    def initUI(self):
        widAddToDeckWindow = QtWidgets.QWidget(self)
        self.setCentralWidget(widAddToDeckWindow)

        #Create The List Widget
        self.deckList = QtWidgets.QListWidget()

        self.deckList.insertItem(0, "Hello")
        self.deckList.insertItem(1, "Hi")
        self.deckList.insertItem(2, "Hello There")

        self.deckList.item(0).setSelected(True)

        self.deckList.itemSelectionChanged.connect(self.show_List)
        print([x.row() for x in self.deckList.selectedIndexes()])

        #Create The Select Deck Button
        self.selectDeck = QtWidgets.QPushButton(self)
        self.selectDeck.setText("Choose")
        
        hboxCreateBottomButtons = QtWidgets.QHBoxLayout()

        hboxCreateBottomButtons.addStretch()
        hboxCreateBottomButtons.addWidget(self.selectDeck)

        #Create The Main VBox
        vboxMain = QtWidgets.QVBoxLayout()
        vboxMain.addWidget(self.deckList)
        vboxMain.addLayout(hboxCreateBottomButtons)        

        widAddToDeckWindow.setLayout(vboxMain)

    def show_List(self):
        print(repr(self.deckList.selectedItems()[0].text()))

def window():
    app = QtWidgets.QApplication(sys.argv)
    win = Add()
    win.show()
    sys.exit(app.exec_())

window()

I've tried using global variables, but it didn't work.

Answer 1

First of all, I recommend you improve your style when naming variables as they make reading easier, for example that the class name are nouns and not a verb.

Getting to the bottom of the problem, never use (or try to use) global variables as they cause silent bugs if there is a better option and you don't understand how it works. In the case that you want a window where you ask the user to provide information on how to select an option that will then be used in the main window then it is advisable to use a QDialog. In the following example, this is done and the "Choose" button is linked to the accept slot so that it closes the window, and that information can be used to know that the "x" button of the window was not closed. Also I have created a property that has the selected text.

import sys

from PyQt5 import QtCore, QtGui, QtWidgets


class MainWindow(QtWidgets.QMainWindow):
    def __init__(self):
        super(MainWindow, self).__init__()
        self.initUI()
        self.setGeometry(1050, 500, 400, 50)
        self.setWindowTitle("Add")

    def initUI(self):
        central = QtWidgets.QWidget(self)
        self.setCentralWidget(central)

        self.deckButton = QtWidgets.QPushButton()
        self.deckButton.setText("Choose")
        self.deckButton.clicked.connect(self.open_deck_browser)

        box = QtWidgets.QVBoxLayout(central)
        box.addWidget(self.deckButton)
        self.label = QtWidgets.QLabel()
        box.addWidget(self.label)
        self.label.hide()

    def open_deck_browser(self):
        dialog = DeckDialog()
        if dialog.exec_() == QtWidgets.QDialog.Accepted:
            self.label.show()
            self.label.setText(dialog.selected_text)


class DeckDialog(QtWidgets.QDialog):
    def __init__(self):
        super(DeckDialog, self).__init__()

        self.initUI()
        self.setGeometry(200, 200, 800, 640)
        self.setWindowTitle("Choose Deck")

    def initUI(self):
        self.deckList = QtWidgets.QListWidget()

        self.deckList.insertItem(0, "Hello")
        self.deckList.insertItem(1, "Hi")
        self.deckList.insertItem(2, "Hello There")

        self.deckList.item(0).setSelected(True)

        self.selectDeck = QtWidgets.QPushButton(self)
        self.selectDeck.setText("Choose")

        hboxCreateBottomButtons = QtWidgets.QHBoxLayout()

        hboxCreateBottomButtons.addStretch()
        hboxCreateBottomButtons.addWidget(self.selectDeck)

        vboxMain = QtWidgets.QVBoxLayout(self)
        vboxMain.addWidget(self.deckList)
        vboxMain.addLayout(hboxCreateBottomButtons)

        self.selectDeck.clicked.connect(self.accept)

    @property
    def selected_text(self):
        items = self.deckList.selectedItems()
        if items:
            return items[0].text()
        return ""


def main():
    app = QtWidgets.QApplication(sys.argv)
    win = MainWindow()
    win.show()
    sys.exit(app.exec_())


if __name__ == "__main__":
    main()