[Python] How can I make a jump function, that won't cause errors? [duplicate]

Making a game on pygame and I have a jump function that won't work about 1/4 of the time

def jump(self):
self.vel_y -= 7
if self.extraJump == True:
self.jumps += 1
self.extraJump = False
self.jumps -=1

def dJump(self):
if king.rect.bottom >= height - 5 and king.rect.bottom <= height +5:
isOnGround = True
else: isOnGround = False
if king.jumps <= 2 and isOnGround:
king.jumps = 2
if pygame.key.get_pressed()[pygame.K_UP] and king.jumps > 0:
now = pygame.time.get_ticks()
if now - self.last >= self.cooldown:
self.last = now
self.jump()

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