pygame errors

[Quentin Bock]

#Space Invaders!
#Title and Icon
pygame.display.set_caption("Space Invaders")
icon = pygame.image.load('space-invaders.png')
pygame.display.set_icon(icon)
#Player
player_Image = pygame.image.load('player.png')
player_X = 370
player_Y = 480

def player():
    screen.blit(player_Image, player_X, player_Y)


#Game Loop
pygame.init()
screen = pygame.display.set_mode((800, 600))
running = True
while running:

    screen.fill((128, 128, 128))

    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            running = False
    player()
    pygame.display.update()

The window will not display the icon, saying, "invalid destination for blit"

Is this an indentation error? I don't understand why this position
would be invalid.

link to tutorial I'm following:

https://www.youtube.com/watch?v=FfWpgLFMI7w