import pygame
from pygame .locals import *
import sys

pygame.init()
display = pygame.display.set_mode((300,300))
FPS_CLOCK = pygame.time.Clock()

flag = 1

while 1:
    for event in pygame.event.get():
        if event.type == QUIT:
            pygame.quit()
            sys.exit() 

        if event.type == pygame.KEYDOWN:
            if event.key == pygame.K_a:
                if flag == 1:
                    pygame.mouse.set_visible(False)
                    flag = 0
                elif flag == 0:
                    pygame.mouse.set_visible(True)
                    flag = 1

    pygame.display.update()
    FPS_CLOCK.tick(30)