This is an example of signal and slot in pyqt

PyQtSignalslotexample.py

import sys
from PyQt5.QtWidgets import QApplication, QWidget, QLabel, QPushButton, QVBoxLayout


def change_button_text():
    button.setText("Button has been clicked")


if __name__ == '__main__':
    
    app = QApplication(sys.argv)

    widget = QWidget()

    v_layout = QVBoxLayout()

    label = QLabel("Sample label")

    button = QPushButton("Button")
    button.clicked.connect(change_button_text)  # The clicked is the signal and you will connect it to a slot using connect method
    
    v_layout.addWidget(label)
    v_layout.addWidget(button)

    widget.setLayout(v_layout)

    widget.show()

    sys.exit(app.exec())