Why does the pygame snake move diagonally?

Question

pygame

Why does the snake move diagonally and not horizontally?

The code

import pygame

pygame.init()

# display settings
width = 650
height = 480
display = pygame.display.set_mode((width, height))
pygame.display.update()
pygame.display.set_caption("Snake Game")

# run loop
run = True

# snake settings
snake_pos = {
  "x": width/2-5,
  "y": height/2-5,
  "x_change": 0,
  "y_change": 0
}

while run:
  for event in pygame.event.get():
    if event.type == pygame.QUIT:
      run = False

    elif event.type == pygame.KEYDOWN:
      if event.key == pygame.K_d:
        snake_pos["x_change"] = 10
        snake_pos["y_change"] = 0
      elif event.key == pygame.K_w:
        snake_pos["x_change"] = -10
        snake_pos["y_change"] = 0
      elif event.key == pygame.K_s:
        snake_pos["x_change"] = 0
        snake_pos["y_change"] = 10
      elif event.key == pygame.K_w:
        snake_pos["x_change"] = 0
        snake_pos["y_change"] = -10

  # snake location
  snake_pos["x"] += snake_pos["x_change"]
  snake_pos["y"] += snake_pos["x_change"]

  # draw snake
  pygame.draw.rect(display, (0, 255, 0), [snake_pos["x"], snake_pos["y"], 10, 10])
  pygame.display.update()

# exit in every occasion
pygame.quit()

Answer 1

Why not do so?

spoiler

import pygame

pygame.init()

WHITE = (255, 255, 255)
BLACK = (0, 0, 0)
RED = (255, 0, 0)
GREEN = (0, 255, 0)
BLUE = (0, 0, 255)


# display settings
width = 650
height = 480
display = pygame.display.set_mode((width, height))
pygame.display.update()
pygame.display.set_caption("Snake Game")

FPS = 60
clock = pygame.time.Clock()

# run loop
run = True

# snake settings
x = 240
y = 325
speed = 5

flR = flL = flUp = fldown = False

while run:
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            run = False

        elif event.type == pygame.KEYDOWN:
            if event.key == pygame.K_d:
                flR = True
                flL = flUp = fldown = False
            elif event.key == pygame.K_w:
                flUp = True
                flR = flL = fldown = False
            elif event.key == pygame.K_s:
                fldown = True
                flR = flUp = flL = False
            elif event.key == pygame.K_a:
                flL = True
                flR  = flUp = fldown = False

  # snake location
    if (flL) and (x > 0):
        x -= speed
    elif (flR) and (x < width):
        x += speed
    elif (flUp) and (y > 0):
        y -= speed
    elif (fldown) and (y < height):
        y += speed

    display.fill(WHITE)
  # draw snake
    pygame.draw.rect(display, (0, 255, 0),
                     (x, y, 10, 10))
    pygame.display.update()
    clock.tick(FPS)

# exit in every occasion
pygame.quit()