python - 名称错误 : global name is not defined in tkinter

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)

为了简洁起见，在这里留下了一些“如果”，但在一些不同的战斗中，这是同样的事情，将按钮命名为 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()

我知道问题是，当我单击“清除”时，所有按钮不一定存在，因此会引发错误...

NameError: global name 'c' is not defined

然后，forget() 中未定义的按钮之后的任何按钮都不会被清除。

在查看了类似的问题后，我发现将变量定义为某种东西，这样即使所有 if 语句都不是 true 并且所有按钮都没有创建，变量至少有一个值。那不起作用，我就会得到

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

我找到了一个解决方法，但这并不是我想要的

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，当我在 map 上有多个按钮/战斗时，如果我只需单击其中任何一个，就会清除 map 。抛出同样的错误，但至少 map 被清除了。我已经尝试过这项工作，但我正在抓狂，感谢您的帮助!

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)

那么你的忘记命令应该是这样的:

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.

您的清晰按钮应如下所示:

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