Simple PyQt5 program to serve as an example/base for future programs.

qt5base.py

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

class MyMainWindow(QMainWindow):
    ''' the main window potentially with menus, statusbar, ... '''

    def __init__(self):
        super().__init__() # calls __init__ of the parent class, QMainWindow
        
        # initialise anything specific to our derived MyMainWindow class
        self.resize(600, 300)
        self.move(300, 200)
        self.setWindowTitle('An empty PyQt QMainWindow')
        self.statusBar().showMessage("Waiting for button")

        central_widget = MyCentralWidget(self)
        self.setCentralWidget(central_widget)

class MyCentralWidget(QWidget):
    ''' everything in the main area of the main window '''

    def __init__(self, main_window): # main_window provided to access parent window 
        super().__init__()
        self.main_window = main_window
        # define left button with method to be called
        left_button = QPushButton('Left', self) # second argument specifies it goes in this widget
        left_button.move(100,100)
        left_button.clicked.connect(self.leftclicked)
        # define right button
        right_button = QPushButton('Right', self)
        right_button.move(700,100)
        right_button.clicked.connect(self.rightclicked)
        # define label
        self.label = QLabel(self)
        self.label.setText("Press a button!")
        self.label.adjustSize()
        
        self.left_times, self.right_times = (0,0)
        
        # place the buttons into a horizontal box layout
        hbox = QHBoxLayout()
        hbox.addWidget(left_button) # add the left button
        hbox.addStretch(1) # add an expanding box 
        hbox.addWidget(right_button) # add the right button
        # place this box and the label into a vertical box layout
        vbox = QVBoxLayout()
        vbox.addStretch(1)
        vbox.addLayout(hbox)
        vbox.addStretch(1)
        vbox.addWidget(self.label)
        #use the box layout as the layout for the window
        self.setLayout(vbox) 

    def leftclicked(self):
        self.main_window.statusBar().showMessage("Left button clicked")
        self.left_times += 1
        self.update_label()

    def rightclicked(self):
        self.main_window.statusBar().showMessage("Right button clicked")
        self.right_times += 1
        self.update_label()
        
    def update_label(self):
        self.label.setText(f"Left: {self.left_times} Right: {self.right_times}")
        self.label.adjustSize()

app = None

def main():
    global app
    app = QApplication(sys.argv)
    w = MyMainWindow()
    w.show() # display the window on the screen (could be included in initUI() instead)
    app.exec() # run the application

if __name__ == '__main__':
    main()