Pygame：如何只运行一次函数，直到密钥被释放？

Question

我正在尝试制作一个平台游戏，我对如何编码它感到困惑，因此无论你持有向上箭头多久，它只会导致y更改一次更改，直到你放开并压制它。（会有是双跳，但我还没有到达那里。我也没有得到引力。）这是我的代码：

import pygame
import time
import random
pygame.init()
display_width = 800
display_height = 600
black = (0,0,0)
white = (255,255,255)
red = (255,0,0)
car_width = 64
gameDisplay = pygame.display.set_mode((display_width,display_height))
pygame.display.set_caption('Platformer')
clock = pygame.time.Clock()
game_loop():
    score = 0
    x = (display_width * 0.45)
    y = (display_height * 0.8)
    y_change = -5
    x_change = 0
    gameExit = False
    while not gameExit:
        for event in pygame.event.get():
            if event.type == pygame.QUIT:
                pygame.quit()
                quit()
            if event.type == pygame.KEYDOWN:
                if event.key == pygame.K_LEFT:
                    x_change = -5
                elif event.key == pygame.K_RIGHT:
                    x_change = 5
                elif event.key == pygame.K_UP:
                    y_change = 25
            if event.type == pygame.KEYUP:
                if event.key == pygame.K_LEFT or event.key == pygame.K_RIGHT:
                    x_change = 0
gameloop()
pygame.quit()
quit()

有人可以帮忙吗？