Python - Pygame名称错误:名称'display_s'没有定义。(bug?) +如何从“作用域”中获取变量

recently began working on a pygame project, and came across this error:

最近开始做一个pygame项目，遇到了这个错误:

Traceback (most recent call last):
  File "GameTesting.py", line 50, in <module>
    screen.blit(display_s, (space_ship_rect.centerx, space_ship_rect.centery))
NameError: name 'display_s' is not defined

Most of the time it pops up, BUT the thing is sometimes it doesn't come up with an error and runs perfectly fine, here's the code: (I commented the parts that are important to this thread)

大多数时候它会弹出，但是有时候它不会出现错误并且运行良好，下面是代码:(我注释了对这个线程很重要的部分)

import sys, pygame, math, time;
from pygame.locals import *;
spaceship = ('spaceship.png')
mouse_c = ('crosshair.png')
backg = ('background.jpg')
fire_beam = ('beams.png')
pygame.init()
screen = pygame.display.set_mode((800, 600))
bk = pygame.image.load(backg).convert_alpha()
mousec = pygame.image.load(mouse_c).convert_alpha()
space_ship = pygame.image.load(spaceship).convert_alpha()
f_beam = pygame.image.load(fire_beam).convert_alpha()
f_beam = pygame.transform.scale(f_beam, (50, 50))
f_beam_rect = f_beam.get_rect()
clock = pygame.time.Clock()
pygame.mouse.set_visible(False)
space_ship_rect = space_ship.get_rect()
space_ship_rect.centerx = 375
space_ship_rect.centery = 300
speed = 3.5
pressed_down = 0
while True:
clock.tick(60)
screen.blit(bk, (0, 0))
for event in pygame.event.get():
    if event.type == QUIT:
        pygame.quit()
        sys.exit()
    elif event.type == MOUSEBUTTONDOWN and event.button == 1:
        global movex
        global movey
        global degs #HERE is where I need movex, movey, degs from below..
                    #This probably won't work, don't even know what global does...
    elif event.type == MOUSEBUTTONDOWN and event.button == 3:
        pressed_down = 1
    elif event.type == MOUSEBUTTONUP:
        pressed_down = 0
    if pressed_down == 1:
        x, y = pygame.mouse.get_pos()
        x1, y1 = x - space_ship_rect.x, y - space_ship_rect.y
        angle = math.atan2(y1, x1)
        dx = speed*math.cos(angle)
        dy = speed*math.sin(angle)
        movex = space_ship_rect.centerx = space_ship_rect.centerx + dx
        movey = space_ship_rect.centery = space_ship_rect.centery + dy
    if event.type == MOUSEMOTION:
        x1, y1 = pygame.mouse.get_pos()
        x2, y2 = space_ship_rect.x, space_ship_rect.y
        dx, dy = x2 - x1, y2 - y1
        rads = math.atan2(dx, dy)
        degs = math.degrees(rads)
        display_s = pygame.transform.rotate(space_ship, (degs)) #ERROR HERE
screen.blit(display_s, (space_ship_rect.centerx, space_ship_rect.centery))#ERROR HERE
pos = pygame.mouse.get_pos()
screen.blit(mousec, (pos))
pygame.display.update()

1 个解决方案

#1

Likely as not, it's NOT having an error when you trigger event.type == MOUSEMOTION - because display_s gets defined.

很可能在触发事件时没有错误。type == MOUSEMOTION -因为display_s被定义了。

If, in the first tick of the game running, you move your mouse, display_s is initialised and therefore you do not get an error. If you do NOT move your mouse, an error occurs.

如果在游戏运行的第一个滴答声中，您移动鼠标，display_s将被初始化，因此不会出现错误。如果不移动鼠标，就会发生错误。

One solution is to create a default value for display_s in your initial level loading code.

一种解决方案是在初始级别加载代码中创建display_s的默认值。

Why you're having a lot of trouble is probably caused by your code structure, or lack thereof.

为什么您会遇到这么多麻烦，可能是由于您的代码结构或者缺少代码结构造成的。

Try refactoring your code, I like to make my game loops look something like:

尝试重构你的代码，我喜欢让我的游戏循环看起来像:

def main():
     load()
     while(playing == True):
         handle_input()
         update()
         draw()
     unload()

#1