Why does the screen stay the same color after pushing the button?

Question

import pygame

pygame.init()
screen = pygame.display.set_mode((700, 700))
pygame.display.set_caption('Checkers')

while True:
  screen.fill((114,157,224))
  pygame.display.update()
  for event in pygame.event.get():
    if event.type == pygame.QUIT:
    pygame.quit()
  elif event.type == pygame.KEYDOWN:
    if event.key == pygame.K_a:
      screen.fill((70,44,133))
      pygame.display.update()

I tried to change pygame.KEYDOWN to pygame.key.get_pressed() but nothing changed.

Answer 1

You should update the display in every frame, but you have to change the Color used to fill the display when the button is pressed:

clock = pygame.time.Clock()
fillColor = pygame.Color(114,157,224)

run = True
while run:
    clock.tick(100)
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            run = False
        elif event.type == pygame.KEYDOWN:
            if event.key == pygame.K_a:
                fillColor = pygame.Color(70,44,133)
  
    screen.fill(fillColor)

    # draw scene
    # [...]
  
    pygame.display.update()

pygame.quit()

The typical PyGame application loop has to:

• limit the frames per second to limit CPU usage with pygame.time.Clock.tick
• handle the events by calling either pygame.event.pump() or pygame.event.get().
• update the game states and positions of objects dependent on the input events and time (respectively frames)
• clear the entire display or draw the background
• draw the entire scene (blit all the objects)
• update the display by calling either pygame.display.update() or pygame.display.flip()