only the arrows keys works in pygame

Question

I am trying to use keyboard inputs on pygame. i figured out how to use the arrows keys with this code:

def events_handler():
    global right, left, up, down
    for event in pygame.event.get():
        if event.type == QUIT:
            pygame.quit()
            sys.exit()
        if event.type == KEYDOWN:
            if event.key == K_RIGHT:
                right = True
            if event.key == K_LEFT:
                left = True
            if event.key == K_UP:
                up = True
            if event.key == K_DOWN:
                down = True
            if event.key == K_RSHIFT:
                plus = True

        if event.type == KEYUP:
            if event.key == K_RIGHT:
                right = False
            if event.key == K_LEFT:
                left = False
            if event.key == K_UP:
                up = False
            if event.key == K_DOWN:
                down = False
            if event.key == K_RSHIFT:
                plus = False

and it work fine but a soon as i change the keys, it stop working. for example if i replace this:

        if event.type == KEYDOWN:
            if event.key == K_RIGHT:
                right = True
      [...]
        if event.type == KEYUP:
            if event.key == K_RIGHT:
                right = False

by this:

        if event.type == KEYDOWN:
            if event.key == K_d:
                right = True
      [...]
        if event.type == KEYUP:
            if event.key == K_d:
                right = False

i also tried others keys like K_PLUS, K_LSHIFT and sevral others but only the arrows keys seems to work. did someone know if this is normal and how to solve this issue ?