Pygame Gui buttons

 import pygame
 import pygame_gui


 pygame.init()

 pygame.display.set_caption('Quick Start')
 window_surface = pygame.display.set_mode((800, 600))

 background = pygame.Surface((800, 600))
 background.fill(pygame.Color('#000000'))

 manager = pygame_gui.UIManager((800, 600))

 hello_button = pygame_gui.elements.UIButton(relative_rect=pygame.Rect((350, 275), (100, 50)),
                                             text='Say Hello',
                                             manager=manager)

 clock = pygame.time.Clock()
 is_running = True

 while is_running:
     time_delta = clock.tick(60)/1000.0
     for event in pygame.event.get():
         if event.type == pygame.QUIT:
             is_running = False

         if event.type == pygame.USEREVENT:
             if event.user_type == pygame_gui.UI_BUTTON_PRESSED:
                 if event.ui_element == hello_button:
                     print('Hello World!')

         manager.process_events(event)

     manager.update(time_delta)

     window_surface.blit(background, (0, 0))
     manager.draw_ui(window_surface)

     pygame.display.update()