pyqt/basic/signals_and_slots_4.py

import sys

from PyQt5.QtWidgets import QMainWindow, QApplication, QLabel, QLineEdit, QWidget, QVBoxLayout


class MainWindow(QMainWindow):

    def __init__(self):
        super().__init__()

        self.setWindowTitle('My App')

        self.label = QLabel()

        self.input = QLineEdit()
        self.input.textChanged.connect(self.label.setText)

        layout = QVBoxLayout()
        layout.addWidget(self.input)
        layout.addWidget(self.label)

        container = QWidget()
        container.setLayout(layout)

        self.setCentralWidget(container)


app = QApplication(sys.argv)
window = MainWindow()
window.show()
sys.exit(app.exec_())