为什么我不能指定默认选择的单选按钮？

Question

我正在使用 Python 的 tkinter 模块制作一个简单的 GUI，但我在使用单选按钮时遇到了很多麻烦。我希望默认选择第一个，但开始时选择其他两个。此外，当我将光标移到 window 上时，第一个被选中（我没有单击），因此所有 3 个都显示为已选中。我的代码：

import tkinter as tk

class openGUI(object):
    def __init__(self):

        # title of window 
        window.title("DUNE LArTPC Simulator")

        # label for choices
        self.question = tk.Label(window, text = "Do you want to create new or analyse existing data?")
        self.question.grid(row = 0, column = 0, columnspan = 3)
        
        # buttons corresponding to choices
        self.createBtn = tk.Button(window, text = "Create", command = self.createData)
        self.analyseBtn = tk.Button(window, text = "Analyse", command = self.analyseData)
        self.createBtn.grid(row = 1, column = 0)
        self.analyseBtn.grid(row = 1, column = 2)

    def analyseData(self):
        """
        Not implemented yet.
        """

        pass 

    def createData(self):
        
        # edit window to display new widgets (irritating to have lots of windows open!)
        window.title("Select variable")
        self.question.destroy()
        self.createBtn.destroy()
        self.analyseBtn.destroy()

        # text in window 
        variableQ = tk.Label(window, text = "Please select Independent variable for dataset:")
        variableQ.grid(row = 0, column = 0, columnspan = 3)

        # radioselect variable  
        selection = tk.StringVar()
        selection.set("lifetime")

        # radioselect buttons 
        lifetimeBtn = tk.Radiobutton(window, variable = selection, value = "lifetime", text = "Lifetime")
        elecNoiseBtn = tk.Radiobutton(window, variable = selection, value = "electronic", text = "Electronic Noise")
        radioactivityBtn = tk.Radiobutton(window, variable = selection, value = "radioactive", text = "Radioactivity")
        lifetimeBtn.grid(row = 1, column = 0)
        elecNoiseBtn.grid(row = 1, column = 1)
        radioactivityBtn.grid(row = 1, column = 2)

# create window 
window = tk.Tk()

# create class object with methods to populate 
# window with widgets 
initWin = openGUI()

# enter mainloop 
window.mainloop()

运行以上给出了我：

我试过使用 lifetimeBtn.select() 方法而不是设置 StringVar()，但这似乎也不起作用。我错过了什么？

编辑：添加了其余代码以展示我如何使用 class 和函数来操作 window。

Answer 1

这是因为selection是createData()函数内部的一个局部变量，函数完成后会被垃圾回收。

将selection更改为实例变量self.selection。

为什么我不能指定默认选择的单选按钮？

Why can't I specific the default selected radiobutton?

python

user-interface

tkinter

radio-button