Python-全局名称未定义

Question

嘿，过去一天我被这个简单的错误难住了，一直没能通过。这是我收到的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)))

但我确实在中定义了它

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。有人能向我解释一下为什么会发生这种情况，以及我应该做些什么来解决它吗？提前感谢

PS：基本上，我在这里想做的是，当按下"下一个"按钮时，它会检查e1和e2，如果其中的字符串与列表中的答案匹配，那么它会随机将另一个图像加载到画布上。

Answer 1

尽管您已经在def button_click_gamescreen（事件）：中声明了pressed的全局变量，但问题是您的def gamesceen（）：def buttonclick_gamescreen[事件]：

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

这里的名称是在函数体内部全局定义的。所以，当我们呼叫：

do_something()
do_somehting_else()

我们明白了，

>>> 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运行时抱怨：

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，请创建一个按下的模块级名称，并在def gamesceen（）：中直接访问它，就像在def button_ckle_gamescreen（event）：所做的那样。基本上是这样的：

global pressed

希望这能有所帮助：）。

Answer 2

您没有在模块级别定义pressed。至少你应该这样做：

pressed = ''
def buttonclick_gamescreen(event):
    global pressed
    ...
def gamescreen():
    ...

或者，您可以将代码重组为一个类：

class Application(tk.Frame):
    def __init__(self, ...):
        self.pressed = ''
    def gamescreen():
        ...
    ...

或者您可以使用StringVar来跟踪该值。

Answer 3

问题是在检查pressed:的位置之前没有执行定义

def gamescreen():
    # ...
    canvas.bind("<Button-1>", buttonclick_gamescreen)  # You only attach callback
    # ...  "pressed" still not defined
    while cdtimer != 0:
        # ...
        if pressed == 8:  # you access "pressed" here
            # ...

要么在模块级别显式定义pressed，要么显式调用buttonclick_gamescreen。