为什么我把pos_stop = mouse_pos注释掉后程序报 未定义pos_stop？（在此代码前我已经获取了鼠标的位置pos_stop = event.pos），而同样在此前获取了鼠标位置的pos_start 却不会报错？
import pygame
import sys
from pygame.locals import *
pygame.init()
size = width, height = 800, 600
bg = (255, 255, 255)
screen = pygame.display.set_mode(size)
pygame.display.set_caption('1111')
turtle = pygame.image.load('sb.png')
clock = pygame.time.Clock()
# 0 -> 未选择，1 -> 选择中，2 -> 完成选择
select = 0
select_rect = pygame.Rect(0, 0, 0, 0)
# 0 -> 未拖拽，1 -> 拖拽中，2 -> 完成拖拽
drag = 0
position = turtle.get_rect()
position.center = width // 2, height // 2
while True:
for event in pygame.event.get():
if event.type == QUIT:
sys.exit()
elif event.type == MOUSEBUTTONDOWN:
if event.button == 1:#按下键盘左键
# 第一次点击，选择范围
if select == 0 and drag == 0:
pos_start = event.pos
select = 1
# 第二次点击，推拽图像
elif select == 2 and drag == 0:
capture = screen.subsurface(select_rect).copy()
cap_rect = capture.get_rect()#传出矩形的各种数据，center
drag = 1
# 第三次点击，初始化
elif select == 2 and drag == 2:
select = 0
drag = 0
elif event.type == MOUSEBUTTONUP:
if event.button == 1:
# 第一次释放，结束选择
if select == 1 and drag == 0:
pos_stop = event.pos
select = 2
# 第二次释放，结束拖拽
if select == 2 and drag == 1:
drag = 2
screen.fill(bg)
screen.blit(turtle, position)
# 实时绘制选择框
if select:
mouse_pos = pygame.mouse.get_pos()
if select == 1:
#pos_stop = mouse_pos#删除次代码就报pos_stop错误：未定义
select_rect.left, select_rect.top = pos_start
select_rect.width, select_rect.height = pos_stop[0] - pos_start[0], pos_stop[1] - pos_start[1]
pygame.draw.rect(screen, (0, 0, 0), select_rect, 1)
# 拖拽裁剪的图像
if drag:
if drag == 1:
cap_rect.center = mouse_pos
screen.blit(capture, cap_rect)
pygame.display.flip()
clock.tick( 30 )
