如何更新 tkinter 子框架类中的标签文本

我在通过按钮命令通过类函数调用更新标签文本时遇到问题。我已将我的根框架分成五个子框架。一旦按钮命令函数被调用并要求用户输入文件。用户输入文件路径显示在根框架中，而不是调用函数的子框架中。在此处输入图片说明

import tkinter as tk
from tkinter import *
from tkinter import filedialog as fd
from tkinter import ttk

LARGE_FONT = ('Verdana', 10)

def donothing():
    print('Do Nothing')


class rootframe(tk.Tk):
    def __init__(self, *args, **kwargs):
        tk.Tk.__init__(self, *args, **kwargs)
        tk.Tk.wm_title(self, "ABC")

        container = tk.Frame(self)
        container.pack(side='top', fill='both', expand=True)
        container.grid_rowconfigure(0, weight=1)
        container.grid_columnconfigure(0, weight=1)

        self.frames = {}
        frame = StartPage(container, self)
        self.frames[StartPage] = frame
        frame.grid(row=0, column=0, sticky='nsew')
        self.show_frame(StartPage)

        for F in (StartPage, graph, piano):
            frame = F(container, self)
            self.frames[F] = frame
            frame.grid(row=0, column=0, sticky='nsew')

        self.show_frame(StartPage)


    def show_frame(self, cont):
        frame = self.frames[cont]
        frame.tkraise()


class StartPage(tk.Frame):
    def __init__(self, parent, controller):
        tk.Frame.__init__(self, parent)

        sidebar = Frame(self, bg='whitesmoke', width=250, height=780,
                        borderwidth=2, relief='ridge')
        statusbar = Frame(self, bg='whitesmoke', width=1280, height=30,
                          borderwidth=2, relief="ridge")
        toolbar = Frame(self, bg='whitesmoke', width=1280, height=30,
                        borderwidth=2, relief='ridge')
        helpbar = Frame(self, bg='whitesmoke', width=1280, height=150,
                        borderwidth=2, relief='ridge')
        mainframe = Frame(self, bg='whitesmoke', width=1280, height=550,
                          borderwidth=2, relief="sunken")
        sidebar.pack(side='left', anchor='sw')
        statusbar.pack(side='bottom', anchor='center')
        toolbar.pack(fill=X, side='top', anchor='center')
        helpbar.pack(side='bottom', anchor='center')
        mainframe.pack(side='top', anchor='center')

        label = tk.Label(toolbar, text='Start Page', font=LARGE_FONT)
        label.pack(side='left', anchor='sw', expand=True)

        button2 = ttk.Button(toolbar, text='File Merge Tool',
                             command=lambda: controller.show_frame(piano))
        button2.pack(side='left', expand=True)
        button3 = ttk.Button(toolbar, text='Graph Page',
                             command=lambda: controller.show_frame(graph))
        button3.pack(side='left', expand=True)


class piano(tk.Frame):

    def __init__(self, parent, controller):
        tk.Frame.__init__(self, parent)
        self.controller = parent
        filename = " "
        sidebar = Frame(self, bg='whitesmoke', width=250, height=780, borderwidth=2,
                    relief='ridge')
        statusbar = Frame(self, bg='whitesmoke', width=1280, height=30,
                      borderwidth=2, relief="ridge")
        toolbar = Frame(self, bg='whitesmoke', width=1280, height=30, borderwidth=2,
                    relief='ridge')
        helpbar = Frame(self, bg='whitesmoke', width=1280, height=150,
                    borderwidth=2, relief='ridge')
        mainframe = Frame(self, bg='whitesmoke', width=1280, height=550,
                      borderwidth=2, relief="sunken")

        sidebar.pack(side='left', anchor='sw')
        statusbar.pack(side='bottom', anchor='center')
        toolbar.pack(fill=X, side='top', anchor='center')
        helpbar.pack(side='bottom', anchor='center')
        mainframe.pack(side='top', anchor='center')

        button2 = ttk.Button(toolbar, text='HOME',
                         command=lambda: controller.show_frame(StartPage))
        button2.pack(side='right', anchor='nw', expand=True)

        label = tk.Label(mainframe, text='File Merge', font=36)
        label.place(x=510, y=10)

        label1 = tk.Label(mainframe, text='file1', font=LARGE_FONT)
        label1.place(x=0, y=60)
        inp1 = ttk.Button(mainframe, text='Browse',
                      command=lambda: piano.readfile())
        inp1.place(x=800, y=60)
        pathlabel = Label(mainframe, background='white', width=80, relief='sunken',
                      borderwidth=4)
        pathlabel.place(x=220, y=60)
        pathlabel.config(text=filename)

        label2 = tk.Label(mainframe, text='file2', font=LARGE_FONT)
        label2.place(x=0, y=80)
        inp2 = ttk.Button(mainframe, text='Browse',
                      command=lambda: piano.readfile())
        inp2.place(x=800, y=80)
        pathlabel1 = Label(mainframe, background='white', width=80, relief='sunken',
                       borderwidth=4)
        pathlabel1.place(x=220, y=80)
        pathlabel1.config(text=filename)

    def readfile():
        filename = fd.askopenfilenames(filetypes=[("TXT Files", "*.txt")])
        pathlabel = Label(background='white', width=80, relief='sunken',
                          borderwidth=4)
        pathlabel.place(x=220, y=60)
        pathlabel.config(text=filename)


class graph(tk.Frame):
    def __init__(self, parent, controller):
        tk.Frame.__init__(self, parent)
        label = ttk.Label(self, text='Graph', font=LARGE_FONT)
        label.pack(pady=10, padx=10)
        button1 = ttk.Button(self, text='Back to Home',
                             command=lambda: controller.show_frame(StartPage))
        button1.pack()


app = rootframe()
app.mainloop()