Newbie question - connect to label PyQt

EarlyBird

Hope that I am right here for PyQt6 question.

After reading the the turoial page: link text, I added a line into the code to change the text for label. See line #18.
Got en error message for this.
How do I connect this? Just for learning purpose, I want to change the displayed text when you click the button.

alt text

Axel Spoerl

Please don't post pictures of text. Add your code directly, using the </> code tags.
You can't pass an argument in a connect statement. You have to define a lambda or a slot, connect to it and do the work there.

EarlyBird

Thank you guys. Will investigate and read some more.

EarlyBird

Thanks for the answer Axel, understood it and now it works:

here my code: I had to move the objects label & line_edit into the main window:

#pyqt6
import sys
from PyQt6.QtWidgets import (QApplication, QWidget, QLineEdit, QPushButton, QVBoxLayout, QLabel)
from PyQt6.QtGui import QPixmap

class MainWindow(QWidget):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        self.setWindowTitle('Qt Signal and Slots')

        button = QPushButton('Click me')
        button2 = QPushButton('Cear Text')
        button3 = QPushButton('Print Text')
        button.clicked.connect(self.button_clicked)
        button2.clicked.connect(self.Clear_Text)
        button3.clicked.connect(self.Print_Text)

        label.setText('Erster Text')
        line_edit.textChanged.connect(label.setText)
        #added Line
        button.clicked.connect(self.Text_Eingabe)

        layout = QVBoxLayout()
        self.setLayout(layout)

        layout.addWidget(button)
        layout.addWidget(button2)
        layout.addWidget(button3)
        layout.addWidget(label)
        layout.addWidget(line_edit)
        self.show()

    def button_clicked(self):
        print('clicked')

    def Text_Eingabe(self):
        print('click')
        label.setText('angeklicked')

    def Clear_Text(self):
        label.clear()
        line_edit.clear()

    def Print_Text(self):
        print(label.text())

if __name__ == '__main__':
    app = QApplication(sys.argv)
    label = QLabel()
    line_edit = QLineEdit()
    window = MainWindow()
    #print(dir(QLineEdit()))
    sys.exit(app.exec())

JonB

@EarlyBird
You have done well grasping the basic of signals & slots.

I had to move the objects label & line_edit into the main window:

You actually moved them out of MainWindow. Your line & line_edit should not be "global" variables. They belong inside your class MainWindow as member variables, use Python self.label & self.line_edit to create them in __init__() and access them from then on inside MainWindow.

@Axel-Spoerl mentioned Python lambdas. Just so you know for your button.clicked.connect(self.button_clicked) you could have written

button.clicked.connect(lambda: print('clicked'))

There are times in the future where you may need to use a lambda like this as an "anonymous" function to connect as a slot.

EarlyBird

Thank you JonB, with your tips, I could change it to anything inside MainWindow.
Do you have a link to a good tutorial explaining lambda:?

Here my latest development:

#pyqt6
import sys
from PyQt6.QtWidgets import (QApplication, QWidget, QLineEdit, QPushButton, QVBoxLayout, QLabel)
from PyQt6.QtGui import QPixmap

class MainWindow(QWidget):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        self.setWindowTitle('Qt Signal and Slots')
        self.setGeometry(100,100,320,210)

        self.label = QLabel()
        self.line_edit = QLineEdit()

        button = QPushButton('Click me')
        button2 = QPushButton('Cear Text')
        button3 = QPushButton('Print Text')
        button.clicked.connect(self.button_clicked)
        button2.clicked.connect(self.Clear_Text)
        button3.clicked.connect(self.Print_Text)

        label2 = QLabel()

        pixmap1 = QPixmap('IMG_0205.JPG')
        pix_label = QLabel()
        pix_label.setPixmap(pixmap1)

        self.label.setText('Erster Text')
        label2.setNum(pixmap1.width())
        self.line_edit.textChanged.connect(self.label.setText)
        #added Line
        button.clicked.connect(self.Text_Eingabe)

        layout = QVBoxLayout()
        self.setLayout(layout)

        layout.addWidget(button)
        layout.addWidget(button2)
        layout.addWidget(button3)
        layout.addWidget(self.label)
        layout.addWidget(self.line_edit)
        layout.addWidget(label2)
        layout.addWidget(pix_label)
        self.show()

    def Text_Eingabe(self):
        print('click')
        self.label.setText('angeklicked')

    def Clear_Text(self):
        self.label.clear()
        self.line_edit.clear()

    def Print_Text(self):
        print(self.label.text())

    def button_clicked(self):
        print('clicked')

if __name__ == '__main__':
    app = QApplication(sys.argv)
    window = MainWindow()
    #print(dir(QLineEdit()))
    sys.exit(app.exec())

JonB

@EarlyBird
Looks better, variables have been moved inside MainWindow.

Lambdas are just a feature of Python, nothing special for Qt. Something like https://www.w3schools.com/python/python_lambda.asp or https://www.geeksforgeeks.org/python-lambda-anonymous-functions-filter-map-reduce/ describes them, or you can look up in any Python documentation.

EarlyBird

Thank you @Axel-Spoerl and @JonB , works great and I understood all including lambda. Great help