Pygame the rectangle is not moving?

Question

Hello I am new to pygame. When I am trying to move my rect right or left. The rectangle does not move from one position to other rather it expands/extends towards right or left.

Why?

import pygame, sys, time

pygame.init()
red = (255, 0, 0)
gameDisplay = pygame.display.set_mode((800, 600))
pygame.display.set_caption('MyGame')
move_x = 200
move_y = 200


while True:
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            pygame.quit()
            quit()
            sys.exit()
        if event.type == pygame.KEYDOWN:
            if event.key == pygame.K_LEFT:
                move_x -= 10

            if event.key == pygame.K_RIGHT:
                move_x += 10
        # pygame.Rect.move(10, 10)
        # gameDisplay.fill(white, rect=[move_x, move_y, 10, 100])
    pygame.draw.rect(gameDisplay, red, [move_x, move_y, 10, 10])
    pygame.display.update()
    pygame.display.flip()

Please see the image above. How it looks like after pressing right or left keys.

Answer 1

Use surface.fill before drawing.

The [0, 0, 0] I used is black in RGB codes. You should declare something like

BLACK = (0, 0, 0)

As a constant to avoid repetition. So please change that and use it like above.

import pygame, sys, time

pygame.init()
red = (255, 0, 0)
gameDisplay = pygame.display.set_mode((800, 600))
pygame.display.set_caption('MyGame')
move_x = 200
move_y = 200


while True:
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            pygame.quit()
            quit()
            sys.exit()
        if event.type == pygame.KEYDOWN:
            if event.key == pygame.K_LEFT:
                move_x -= 10

            if event.key == pygame.K_RIGHT:
                move_x += 10
        # pygame.Rect.move(10, 10)
    gameDisplay.fill([0,0,0]) # The line added.
    pygame.draw.rect(gameDisplay, red, [move_x, move_y, 10, 10])
    pygame.display.update()
    pygame.display.flip()

Be careful not to draw anything before the fill method, it will be erased because you filled the screen with something else.

Edit: I just realized you already defined red. It is probably better if you declared it all caps. RED. Because it is a global constant as PEP-8 suggests.

Answer 2

import pygame, sys, time

pygame.init()
red = (255, 0, 0)

gameDisplay = pygame.display.set_mode((800, 600))
background = pygame.Surface(gameDisplay.get_size())
background = background.convert()
background.fill((0,0,0))

pygame.display.set_caption('MyGame')

move_x = 200
move_y = 200

while True:
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            pygame.quit()
            quit()
            sys.exit()
        if event.type == pygame.KEYDOWN:
            if event.key == pygame.K_LEFT:
                move_x -= 10

            if event.key == pygame.K_RIGHT:
                move_x += 10
        # pygame.Rect.move(10, 10)
        # gameDisplay.fill(white, rect=[move_x, move_y, 10, 100])


    background.fill((0,0,0))
    pygame.draw.rect(background, red, [move_x, move_y, 10, 10])

    gameDisplay.blit(background, (0, 0))
    pygame.display.flip()