Python - 全局名称未定义

Question

嘿，过去一天我一直被这个简单的错误所困扰，并且无法通过它。这是我收到此错误消息的代码部分:

Exception in Tkinter callback
Traceback (most recent call last):
  File "/usr/lib/python3.2/tkinter/__init__.py", line 1402, in __call__
    return self.func(*args)
  File "/home/ppppwn3d/workspace/Python/JailBreakBob/JailBreakBob.py", line 110, in buttonclick_mainscreen
    gamescreen()
  File "/home/ppppwn3d/workspace/Python/JailBreakBob/JailBreakBob.py", line 58, in gamescreen
    if pressed == 8 and e1 == answerlistx[randomimage] and e2 == answerlisty[randomimage]:
NameError: global name 'pressed' is not defined

内部

def gamescreen():
    imagelist = ["1.gif","2.gif","3.gif","4.gif","5.gif","6.gif","7.gif","8.gif","9.gif","10.gif","11.gif","12.gif","13.gif","14.gif","15.gif","16.gif","17.gif","18.gif","19.gif","20.gif","21.gif","22.gif","23.gif","24.gif","25.gif","26.gif","27.gif","28.gif","29.gif","30.gif","31.gif","32.gif","33.gif","34.gif","35.gif","36.gif","37.gif","38.gif","39.gif","40.gif","41.gif","42.gif","43.gif","44.gif","45.gif","46.gif","47.gif","48.gif","49.gif","50.gif"]
    answerlistx = [-1, -3, 3, 4, -7, 8, 9, 10, -10, 2, -7, 7, -1, -5, -6, -9, -7, 10, -4, 8, 1, -8, -10, -1, -3, -7, -3, 7, 3, -4, 1, -8, -4, 9, -5, -10, 10, 2, 2, -10, 4, 9, -3, 6, 10, -6, 4, 9, -10, -10]
    answerlisty = [3, -6, -5, 3, -2, 4, -4, -3, 4, -6, 1, 2, 2, 3, 2, -1, -5, 1, -3, 1, -2, -2, -5, -3, -2, -6, -3, 6, 2, 0, -5, 6, -4, 4, 1, -6, 0, -6, 5, 2, 4, -4, -2, 0, -3, -6, -4, 1, -3, 1]

    canvas.bind("<Button-1>", buttonclick_gamescreen)
    canvas.pack(expand = YES, fill = BOTH)
    photo = PhotoImage(file="gamescreen.gif")
    canvas.create_image(1, 1, image = photo, anchor = NW)
    e1 = Entry(canvas, width = 11)
    e2 = Entry(canvas, width = 11)
    canvas.create_window(390, 501, window=e1, anchor = NW)
    canvas.create_window(551, 501, window=e2, anchor = NW)
    canvas.after(1, countdowntimer)
    while cdtimer != 0:
        randomimage = random.randrange(0,49+1)
        game = PhotoImage(file=imagelist[randomimage])
        images = canvas.create_image(30, 65, image = game, anchor = NW)
        if pressed == 8 and e1 == answerlistx[randomimage] and e2 == answerlisty[randomimage]:
             canvas.delete(images)
             randomimage = random.randrange(0,49+1)
             scorecounter = scorecounter + 1
             game = PhotoImage(file=imagelist[randomimage])
             images = canvas.create_image(30, 65, image = game, anchor = NW)
        elif pressed == 8 and e1 != answerlistx[randomimage] or e2 !=     answerlisty[randomimage]:
            wronganswer = canvas.create_text(400, 200, text="Incorrect", font="Ubuntu 29 bold", fill=red, anchor=NW)
            e1.delete(0.0,END)   
            e2.delete(0.0,END)
            canvas.after(1500,(canvas.delete(wronganswer)))

但我确实定义了它

def buttonclick_gamescreen(event):
    global pressed
    pressed = ""

    if event.x >853 and event.x <957 and event.y > 8 and event.y < 56 : pressed = 7 
    if event.x >666 and event.x <947 and event.y > 491 and event.y < 534 : pressed = 8 
    if pressed == 7 :
        window.destroy()
    if pressed == 8:
        print("next button")

这让我很困惑。有人可以向我解释一下为什么会发生这种情况以及我应该采取什么措施来解决它吗？提前致谢

PS:基本上我在这里想做的是，当按下“下一个”按钮时，它将检查 e1 和 e2，如果那里的字符串与列表中的答案匹配，那么它将随机加载另一个图像到 Canvas 。

Answer 1

尽管您已在 def buttonclick_gamescreen(event): 中声明了按下的全局变量，但问题是您的 def gamescreen(): 在 def buttonclick_gamescreen: 之前被调用(事件):，因此Python运行时无法在内存中查找名为pressed的引用，因为该行代码从未被执行过。为了演示这是如何影响的，请考虑以下内容:

def do_something():
    global name
    name = 10
    print name

def do_somehting_else():
    if name == 10:
        print "Valid"

这里的 name 在函数体内定义为全局的。因此，当我们调用:

do_something()
do_somehting_else()

我们得到，

>>> 10
>>> Valid

但是，如果我们将函数调用的顺序更改为:

do_somehting_else()
do_something()

Python 运行时提示:

Traceback (most recent call last):
  File "/home/rahul/workspace/PyTest/func.py", line 94, in <module>
    do_somehting_else()
  File "/home/rahul/workspace/PyTest/func.py", line 91, in do_somehting_else
    if name == 10:
NameError: global name 'name' is not defined

要解决这个问题，如果函数调用在您的控制范围内，请按正确的顺序执行它们。如果没有，请创建一个模块级别名称按下并直接在 def gamescreen(): 中访问它，就像在 def buttonclick_gamescreen(event): 中所做的那样。基本上是这样的:

global pressed

希望这有帮助:)。