如何更新tkinter子框架类中的标签文本

import tkinter as tk

class SubFrame(tk.Frame):
    def __init__(self, parent):
        tk.Frame.__init__(self, parent)
        self.label = tk.Label(self, text="初始文本")
        self.label.pack()

    def update_label_text(self, new_text):
        self.label.config(text=new_text)

root = tk.Tk()
sub_frame = SubFrame(root)
sub_frame.pack()

sub_frame.update_label_text("新的文本")