Proper way to pass an infromation/variable across QTabWidgets?

Question

EDIT: Changed title, few mistakes in code were resolved (now working properly)

The GUI I am trying to make will be a simple QTabWidget, leading a user straightforwardly towards the end tab by tab.

For now, I have three *.py files - main.py, tab1.py, tab2.py. In main.py is the main window of the app and function to run the app like this (simplified just to focus on my question):

import sys
import tab1
import tab2
import PyQt5.QtWidgets as qtw

def main():
    app = qtw.QApplication(sys.argv)
    window = MainWindow()
    window.show()
    sys.exit(app.exec_())

class MainWindow(qtw.QmainWindow):
    def __init__(self):
        super().__init__()
        self.tabwidget = qtw.QTabWidget()
        self.setCentralWidget(self.tabwidget)

        self.tab1 = tab1.Tab_1()
        self.tab2 = tab2.Tab_2()

        # This is how I now passing the information from tab1 to tab2
        self.tab1.path_line.textChanged.connect(self.tab2.path_widget.setText)

        self.tabwidget.addTab(self.tab1, 'tab1')
        self.tabwidget.addTab(self.tab2, 'tab2')

if __name__ == '__main__':
    main()

In the tab1.py is defined class for a tabwidget which will serve as an input data tab. There is a button to open filedialog, read filename, and write the path into QLineEdit widget:

import PyQt5.QtWidgets as qtw

class Tab_1(qtw.QWidget):
    def __init__(self):
        super().__init__()
        self.path_line = qtw.QLineEdit()
        self.but = qtw.QPushButton('Open')
        self.but.clicked.connect(self.openfile)

        layout_1 = qtw.QVBoxLayout()
        layout_1.addWidget(self.but)
        self.setLayout(layout_1)

    def openfile(self):
        filename, _ = qtw.QFileDialog.getOpenFileName(self, 'Title', 'File types')
        if filename:
            self.path_line.setText(filename)
        else:
            self.path_line.setText('No file was selected!')

Now I want to in another file tab2.py use the path I got from qtw.OpenFileDialog. So the defined class Tab_2() looks like this:

import PyQt5.QtWidgets as qtw

class Tab_2(qtw.QWidget):
    def __init__(self):
        super().__init__()

        # Retrieving the information by QLabel widget
        self.path_widget = qtw.QLabel()
        # Transform the information into string variable
        self.path_string = self.path_widget.text()
        
        layout_2 = qtw.QVBoxLayout()
        layout_2.addWidget(self.path_widget) # The path from QFileDialog (Tab1) should appered on Tab2
        self.setLayout(layout_2)

My question is, is this the proper way to do it? Should I use MainWindow class as a "getter" and "passer" of the information like that or should that be implemented in the tab classes themselves? It works but I do not want to learn to do something bad way and eventually get used to it. I understand classes and their inheritance to some point (a lot of examples of dog classes or employee classes that I understand how it works but in my case I am confused). In combination with GUI, it messing up my head. Also, I want to have each tab as a separate class in a separate *.py file to make it clear and easy to add another one in the future. I see, that it might not be the right way to uses classes but each tab will have a different layout.

Answer 1

Basically your code works.

To write the selected path, you use the QLineEdit widget of the Tab_1 class. You don't show the path_line widget itself anywhere, but use the textChanged signal.

It is not clear why there is a path_string object in the Tab_2 class that you are not using.

I would suggest you:

• object self.path_line = '' declare in the MainWindow class.

• use the currentChanged signal:

  self.tabwidget.currentChanged.connect(self.current_changed)

• when creating instances of the Tab_1 and Tab_2 classes, pass self as an argument, which will allow you to have access to objects of the MainWindow class in these widgets, for example path_line.

• In the slot current_changed, you can write logic, which you will need when the index of the current page changes.

---

import sys
import PyQt5.QtWidgets as qtw

#from tab1 import Tab_1
class Tab_1(qtw.QWidget):
    def __init__(self, parent=None):                                 # + parent
        super().__init__()
        self.parent = parent                                         # + parent

        self.but = qtw.QPushButton('Open')
        self.but.clicked.connect(self.open_file)

        layout = qtw.QVBoxLayout(self)
        layout.addWidget(self.but)

    def open_file(self):
        filename, _ = qtw.QFileDialog.getOpenFileName(self, 'Title', 'File types')
        if filename:
            self.parent.path_line = filename                         # + parent
        else:
            self.parent.path_line = ''                               # + parent
 
 
#from tab2 import Tab_2
class Tab_2(qtw.QWidget):
    def __init__(self, parent=None):
        super().__init__()
        self.parent = parent

        self.path_widget = qtw.QLabel()
        
        layout = qtw.QVBoxLayout(self)
        layout.addWidget(self.path_widget) 
       

class MainWindow(qtw.QMainWindow):
    def __init__(self):
        super().__init__()
        self.path_line = ''                                          # + path_line
        
        self.tabwidget = qtw.QTabWidget()
        self.tabwidget.currentChanged.connect(self.current_changed)  # + currentChanged
        self.setCentralWidget(self.tabwidget)
        
        self.tab1 = Tab_1(self)                                      # + self
        self.tab2 = Tab_2(self)                                      # + self

        self.tabwidget.addTab(self.tab1, 'Tab 1')
        self.tabwidget.addTab(self.tab2, 'Tab 2')
        
    def current_changed(self, index):
        if index == 0:
            self.statusBar().showMessage('Message in statusbar. '
                'Select the file to read.', 5000)
        if index == 1:
            self.tab2.path_widget.setText(self.path_line)
            if not self.path_line:
                self.statusBar().showMessage(
                    'Go to the first tab and select the file to read.', 5000)            
            

def main():
    app = qtw.QApplication(sys.argv)
    window = MainWindow()
    window.resize(400, 300)
    window.show()
    sys.exit(app.exec_())
    
if __name__ == '__main__':
    main()

Answer 2

Building on the answer by S.Nick, I would suggest something along the lines of:

    import sys
    import PyQt5.QtWidgets as qtw
    
    #from tab1 import Tab_1
    class Tab_1(qtw.QWidget):
        def __init__(self, parent=None):                                 # + parent
            super().__init__()
            self._parent = parent                                         # + parent
    
            self.but = qtw.QPushButton('Open')
            self.but.clicked.connect(self.open_file)
    
            layout = qtw.QVBoxLayout(self)
            layout.addWidget(self.but)
    
        def open_file(self):
            filename, _ = qtw.QFileDialog.getOpenFileName(self, 'Title', 'File types')
            if filename:
                self._parent.path_line = filename                         # + parent
            else:
                self._parent.path_line = ''                               # + parent
     
     
    #from tab2 import Tab_2
    class Tab_2(qtw.QWidget):
        def __init__(self, parent=None):
            super().__init__()
            self._parent = parent
    
            self.path_widget = qtw.QLabel()
            
            layout = qtw.QVBoxLayout(self)
            layout.addWidget(self.path_widget) 
           
    
    class MainWindow(qtw.QMainWindow):
        def __init__(self):
            super().__init__()
            self.path_line = ''                                          # + path_line
            
            self.tabwidget = qtw.QTabWidget()
            self.tabwidget.currentChanged.connect(self.current_changed)  # + currentChanged
            self.setCentralWidget(self.tabwidget)
            
            self.tab1 = Tab_1(self)                                      # + self
            self.tab2 = Tab_2(self)                                      # + self
    
            self.tabwidget.addTab(self.tab1, 'Tab 1')
            self.tabwidget.addTab(self.tab2, 'Tab 2')

            
        def current_changed(self, index):
            if index == 0:
                self.statusBar().showMessage('Message in statusbar. '
                    'Select the file to read.', 5000)
            if index == 1:
                self.tab2.path_widget.setText(self.path_line)
                if not self.path_line:
                    self.statusBar().showMessage(
                        'Go to the first tab and select the file to read.', 5000)            
                
    
    def main():
        app = qtw.QApplication(sys.argv)
        window = MainWindow()
        window.resize(400, 300)
        window.show()
        sys.exit(app.exec_())
        
    if __name__ == '__main__':
        main()

Note that tab1.parent() returns a different thing than tab1._parent. To get the instance of MainWindow, you need to call parent three times: tab1.parent().parent().parent() or use tab1.window() instead.

That is to say,

    print(self.tab1.parent())
    print(self.tab1.parent().parent())
    print(self.tab1.parent().parent().parent())
    print(self.tab1.window())

produces

<PyQt5.QtWidgets.QStackedWidget object at 0x00000245A7A08310>
<PyQt5.QtWidgets.QTabWidget object at 0x00000245A60DFE20>
<__main__.MainWindow object at 0x00000245A60DFD90>
<__main__.MainWindow object at 0x00000245A60DFD90>