Pygame and pygame.time.wait() function is working in a bizarre way

Question

I am trying to change the pygame screen. First, I draw a rect. Then, I fill the screen again. In-between I add wait function to see the change. When I run program, screen starts black and waits for every wait function without doing any changes. Then, it shows the end result.

import pygame
BlockList=[]
pygame.init()
block_side_length=30
black = 0,0,0
GameArea_start_x=5
GameArea_start_y=5
GameArea_width=300
GameArea_height=270
gameDisplay = pygame.display.set_mode((400,300))
pygame.display.set_caption("Tetris")
gameDisplay.fill((0,100,100))
GameArea = pygame.draw.rect(gameDisplay,black,[GameArea_start_x,GameArea_start_y,GameArea_width,GameArea_height])
lowest_block_y =GameArea_start_y+GameArea_height-block_side_length
pygame.time.wait(2000)
gameDisplay.fill((0,100,100))
pygame.draw.rect(gameDisplay,(0,250,0),[50,50,40,90])
pygame.time.wait(2000)
gameDisplay.fill((0,100,100))
GameArea

Output:

After 4 secs

Note: I am trying to draw the rectangle by calling its name. It doesn't work. Is there any similar fashion?

Answer 1

In order to update what is shown in the pygame window, you must call pygame.display.update(), like so:

import pygame
BlockList=[]
pygame.init()
block_side_length=30
black = 0,0,0
GameArea_start_x=5
GameArea_start_y=5
GameArea_width=300
GameArea_height=270
gameDisplay = pygame.display.set_mode((400,300))
pygame.display.set_caption("Tetris")
gameDisplay.fill((0,100,100))
GameArea = pygame.draw.rect(gameDisplay,black,[GameArea_start_x,GameArea_start_y,GameArea_width,GameArea_height])
lowest_block_y =GameArea_start_y+GameArea_height-block_side_length
pygame.display.update()
pygame.time.wait(2000)
gameDisplay.fill((0,100,100))
pygame.draw.rect(gameDisplay,(0,250,0),[50,50,40,90])
pygame.display.update()
pygame.time.wait(2000)
gameDisplay.fill((0,100,100))
pygame.display.update()

Note that your approach of calling pygame.time.wait() for long periods of time will cause the window to freeze and become unresponsive while waiting. Some better approaches are described in this stackoverflow question.