nameerror：全局名称不Tkinter的定义

Question

# -*- coding: utf-8 -*- 
from Tkinter import * 
import Image, ImageTk 
import test2 

root = Tk() 
root.wm_title("InterActMap") 

def get(): 


    global CountryName 
    CountryName = e1.get() 
    global Day 
    Day = e2.get() 
    global Month 
    Month = e3.get() 
    global Year 
    Year = e4.get() 
    Monthint=int(Month) 
    Dayint=int(Day) 
    Yearint=int(Year) 

    if CountryName == "germany" and Monthint == 8 and Dayint == 26 and Yearint == 1914: 
    global a 
     a = Button(root, bg = "red", text ="Battle of Tannenberg" , command=None) 
     a.place(x=691, y=229) 
     test2.register(a, Tannenberg) 

留下了几个，如果这里出去brevitys缘故，而是与几个不同的战役同样的事情，命名按钮A，B，C，d，E，F等。

def forget(): 
    a.place_forget() 
    b.place_forget() 
    c.place_forget() 
    d.place_forget() 
    f.place_forget() 


canvas = Canvas(root, width = 1280, height=720) 

country = Label(root, text = "Country") 
country.place(x=5, y=5) 
e1 = Entry(root) 
e1.place(x=60,y=5) 

day = Label(root, text = "Day") 
day.place(x=230, y=5) 
e2 = Entry(root) 
e2.place(x=260, y=5) 

month = Label(root, text = "Month") 
month.place(x=430, y=5) 
e3 = Entry(root) 
e3.place(x=475, y=5) 

year = Label(root, text = "Year") 
year.place(x=645, y=5) 
e4 = Entry(root) 
e4.place(x=680, y=5) 



File = "map1.jpg" 
img = ImageTk.PhotoImage(Image.open(File)) 
canvas.create_image(0,0,image=img,anchor="nw") 

Button1 = Button(root, text = "Submit", command=get) 
Button1.place(x=850, y=5) 
Button2 = Button(root, text = "Clear", command=forget) 
Button2.place(x=925, y=5) 
Button3 = Button(root, text = "Exit", command=root.quit) 
Button3.place(x=960, y=5) 




canvas.pack() 
root.mainloop() 

我知道的问题是，当我点击清除所有按钮不必然存在所以它抛出一个错误...

NameError: global name 'c' is not defined 

然后任何按钮忘记（）一前一后未定义的内容不会被清除。

环顾了类似的问题后，我发现将变量定义为某些东西，即使所有的if语句都不是真且所有的按钮都没有创建，变量至少也有一个值。没有工作，我只想得到

AttributeError: 'NoneType' object has no attribute 'forget' 

我想出了一个解决办法，但它不是真的是我想要

if CountryName == "germany" and Monthint == 8 and Dayint == 26 and Yearint == 1914: 
    global a 
     a = Button(root, bg = "red", text ="Battle of Tannenberg" , command=forget) 
     a.place(x=691, y=229) 
     test2.register(a, Tannenberg) 

有了这个，当我有多个按钮/战斗在地图上，如果我只要点击它们中的任何一个就可以清除地图。同样的错误被抛出，但至少地图被清除。 我试着做这个工作，但我拉我的头发，感谢任何帮助！

Answer 1

最好的办法是创建一个包含所有按钮的实例级列表。例如：

button_list = [] 

if CountryName == "germany" and Monthint == 8 and Dayint == 26 and Yearint == 1914: 
    a = Button(root, bg = "red", text ="Battle of Tannenberg" , command=None) 
    a.place(x=691, y=229) 
    button_list.append(a) 

然后你忘了命令应该是这样的：

def forget(lst_to_clear): 
    for button in reversed(lst_to_clear): 
     button.place_forget() 
     lst_to_clear.pop() 
     # the reversal is to make sure popping the item out of the 
     # original list doesn't break the for loop. You could just 
     # as easily do: 
     # # while lst_to_clear: 
     # #  lst_to_clear.pop().place_forget() 
     # but I find it a little less readable. 

和您的Clear按钮应该是这样的：

Button2 = Button(root, text = "Clear", command=lambda: forget(button_list)) 
Button2.place(x=925, y=5) 

Answer 2

所以你可以在这种情况下使用try/except处理程序。小例子：

from tkinter import * 

root = Tk() 

def forget() 
    for x in (a, b, c, d, e, f, g): 
     try: 
      x.place_forget() 
     except NameError: 
      pass 

a = Button(text = 'hi', command = forget) 
a.place(x = 0, y = 0) 

root.mainloop() 

这里的代码会返回一个NameError因为b，c，d等，不要再exist.The异常与此交易，这样你就不会中断。

希望能帮到你！