在Python GUI中更改按钮颜色

Question

import sys
from tkinter import *

def run_GUI():
    # create the window
    root = Tk()
    frame = Frame(root)
    frame.pack()

    #modify root window
    root.title("Simple GUI")
    root.geometry("700x300") # w x h        
    def SP2T():     # Edit occurs here where I forgot to pit that the button was created in a called funtction
        #Creates Row
        frameSP2T = Frame(root)
        frameSP2T.pack(side = TOP)

        #Creating Buttons First Row
        button1 = Button(frameSP2T, padx=13, pady = 6, bd=4, text="SW02",fg = "black", command = SW02)
        button1.pack(side = LEFT)

    def SW02():
        print("SW02 is on")
        button1["fg"] = "green"

    #Sets up initial boot screen
    #Creates Row
    topframe = Frame(root)
    topframe.pack(side = TOP)

    #Creating Buttons First Row
    buttonA = Button(topframe, padx=13, pady = 6, bd=4, text="SP2T",fg = "black", command = SP2T)
    buttonA.pack(side = LEFT)

    buttonB = Button(topframe, padx=12, pady = 6, bd=4, text="SP4T",fg = "black")
    buttonB.pack(side = LEFT)

    buttonC = Button(topframe, padx=12, pady = 6, bd=4, text="SP12T",fg = "black")
    buttonC.pack(side = LEFT)

    buttonD = Button(topframe, padx=12, pady = 6, bd=4, text="QUIT", fg="red",command=frame.quit)
    buttonD.pack(side = LEFT)

    #Kick off event loop
    root.mainloop()
    return

run_GUI()

我遇到了这个错误：

Traceback (most recent call last):

  File "C:\Python34\lib\tkinter\__init__.py", line 1487, in __call__

   return self.func(*args)

   File "C:\Python34\gui_attempt.py", line 25, in SW02

   button1["fg"] = "green"

NameError: name 'button1' is not defined

这是更新后的版本，希望能展示整个情况

这个程序还有更多内容，所以提到的是第60行，但这里是问题所在。我想在按钮被按下时改变它的颜色。

Answer 1

你遇到了一个关于作用域的问题。这个错误发生在SW02()这个函数里，因为你试图修改一个不在这个函数范围内的对象。你需要把这个对象传递进来。把SW02()改成下面这样：

def SW02(button1):
    print("SW02 is on")
    button1["fg"] = "green"

因为你把这个函数当作命令的动作，所以你有几种方法可以把对象传递进去。

可以使用一个lambda表达式：

button1 = Button(frameSP2T, padx=13, pady = 6, bd=4, text="SW02",fg = "black", command = lambda: SW02(button1))

也可以使用functools.partial：

from functools import partial
# other stuff
_SW02 = partial(SW02, button1)
button = Button(frameSP2T, padx=13, pady = 6, bd=4, text="SW02",fg="black", command=_SW02)

另外，正如jonrsharpe的回答中提到的，你可以把整个图形用户界面（GUI）函数重构成一个类，把所有的控件作为类的成员，然后把控件的操作和类的方法关联起来，而不是用普通的函数。这样，所有修改GUI组件的函数都能访问到这些组件。

Answer 2

最简单的解决办法是在需要访问那个对象的两个函数开头加上 global button。

def SP2T():
    global button1
    ...

def SW02():
    global button1
    ...

不过，使用 global 通常不是个好主意——你可以考虑用面向对象的方法，像下面这个简单的例子：

import tkinter as tk

class MyGui(tk.Tk):

    def __init__(self):
        super(MyGui, self).__init__()
        self.create_widgets()


    def create_widgets(self):
        self.frame = tk.Frame(self)
        self.frame.pack()
        self.buttonA = tk.Button(self.frame, padx=13, pady=6, bd=4, text="SP2T",
                                 fg="black", command=self.SP2T)
        self.buttonA.pack(side=tk.LEFT)

    def SW02(self):
        print("SW02 is on")
        self.button1["fg"] = "green"

    def SP2T(self):
        self.button1 = tk.Button(self.frame, padx=13, pady=6, bd=4, text="SW02",
                                 fg="black", command=self.SW02)
        self.button1.pack(side=tk.LEFT)

if __name__ == "__main__":
    root = MyGui()
    root.mainloop()