Python - Pygame名称错误：名称'display_s'未定义。 （错误？）+如何从内部“范围” GET变量

Question

最近开始在pygame的项目工作，以及跨越这个错误传来：

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 

它的大部分弹出的时间，但事情是有时候它并没有拿出一个错误，并且运行完全正常，下面的代码：（我评论说是很重要的这个线程的部分）

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() 

Answer 1

几率是不是，当你触发它不是有错误event.type == MOUSEMOTION - 因为display_s被定义。

如果在游戏运行的第一个刻度中移动鼠标，则会初始化display_s，因此您不会收到错误。如果您不移动鼠标，则会发生错误。

一种解决方案是在初始级别加载代码中为display_s创建默认值。

为什么你遇到很多麻烦可能是由你的代码结构造成的，或者是由于它的缺乏。

尝试refactoring你的代码，我喜欢让我的游戏循环类似于：

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