PyQt

Basic

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


def on_button_click():
    alert = QMessageBox()
    alert.setText("You've clicked this button!")
    alert.exec()


app = QApplication([])
root = QWidget()
layout = QVBoxLayout()

label = QLabel("Test")
layout.addWidget(label)

button = QPushButton("Click me!")
button.clicked.connect(on_button_click)
layout.addWidget(button)

root.setLayout(layout)
root.show()
app.exec()

Simple menu

from PyQt5.QtWidgets import QAction, QApplication, QMainWindow, QPlainTextEdit, QVBoxLayout, QWidget


app = QApplication([])
app.setApplicationName("Text Editor")

text_edit = QPlainTextEdit()
window = QMainWindow()
window.setWindowTitle("Text Editor")
window.setCentralWidget(text_edit)

menu = window.menuBar().addMenu("&File")
close = QAction("&Close")
close.triggered.connect(window.close)
menu.addAction(close)

window.show()
app.exec()