Pygame rect 不会更新

Question

I am building a game in pygame where there is a red target that moves up and down on the right side of the screen and a ship on the left side of the screen the moves up and down that fires bullets (which is just a blue rectangle) at the target.

My ship, and my target start in the center of each side of the screen and are properly moving. The problem that I have is when I 'fire' a bullet the bullet is getting drawn at the ship's original position, not where the ship has moved to on the screen.

I have the bullet's rect set to the ship image's rect outside of my while loop, but I would think that it would get updated as my ship moves up and down on the screen.

import pygame
import pygame.sprite
import sys

screen_width = 1200
screen_height = 800
screen = pygame.display.set_mode((screen_width, screen_height))
screen_rect = screen.get_rect()

image = pygame.image.load('ship.bmp')
image_rect = image.get_rect()
image_rect.midleft = screen_rect.midleft

target_rect = pygame.Rect(400, 0, 100, 100)
target_color = (255, 0, 0)
target_rect.midright = screen_rect.midright
target_direction = 1

bullet_rect = pygame.Rect(0, 0, 15, 3)
bullet_rect.midright = image_rect.midright
bullet_color = (0, 0, 255)
fire_bullet = False


while True:

    screen.fill((0, 255, 0))

    for event in pygame.event.get():
        if event.type == pygame.KEYDOWN:
            if event.key == pygame.K_q:
                sys.exit()

            # Move the ship up and down 
            elif event.key == pygame.K_UP:
                image_rect.y -= 45
            elif event.key == pygame.K_DOWN:
                image_rect.y += 45                
            # Active bullet fired 
            elif event.key == pygame.K_SPACE:
                fire_bullet = True

        elif event.type == pygame.QUIT:
                sys.exit()

    # Move the bullet across the screen if fired
    if fire_bullet:
        screen.fill(bullet_color, bullet_rect)
        bullet_rect.x += 1

    # Move the Target up and down
    target_rect.y += target_direction
    if target_rect.bottom >= screen_height:
        target_direction *= -1
    elif target_rect.top <= 0:
        target_direction *= -1


    screen.fill(target_color, target_rect)
    screen.blit(image, image_rect)
    pygame.display.flip()

Answer 1

I have the bullet's rect set to the ship image's rect outside of my while loop, but I would think that it would get updated as my ship moves up and down on the screen.

That's not it. You just set the position of the rect, there is not automatic update. You have to write the code to keep them in sync.
But even simpler, in your case you could create the bullet rect when you shot. Move the bullet creation in the loop like this:

elif event.key == pygame.K_SPACE:
    bullet_rect = pygame.Rect(0, 0, 15, 3)
    bullet_rect.midright = image_rect.midright
    bullet_color = (0, 0, 255)
    fire_bullet = True