名称错误： 未定义名称"clear_message"

Question

from Tkinter import *
import tkinter as tk   # python3
TITLE_FONT = ("Helvetica", 18, "bold")

class SampleApp(tk.Tk):
    def __init__(self, *args, **kwargs):
        tk.Tk.__init__(self, *args, **kwargs)
        # the container is where I stack a bunch of frames
        # on top of each other, then the one we want visible
        # will be raised above the others
        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 = {}
        for F in (MainPage,StorageOrMotor,Storage,Motor):
            page_name = F.__name__
            frame = F(container, self)
            self.frames[page_name] = frame
            # put all of the pages in the same location;
            # the one on the top of the stacking order
            # will be the one that is visible.
            frame.grid(row=0, column=0, sticky="nsew")
        self.show_frame("MainPage")
    def show_frame(self, page_name):
        '''Show a frame for the given page name'''
        frame = self.frames[page_name]
        frame.tkraise()

class MainPage(tk.Frame):
    global user_key
    global psw_key
    user_key=""
    psw_key=""
#Here is the defined for clear_message `def`   
    def clear_message():
        user_key.delete(0, 'END')
        psw_key.delete(0, 'END')
    def __init__(self, parent, controller):
        tk.Frame.__init__(self, parent)
        self.controller = controller
        Username = tk.Label(self, text="Username:",font=("Helvetica", "20","bold"))
        Username.grid(row=2, column=3,columnspan=2)
        Password = tk.Label(self, text="Password:",font=("Helvetica", "20","bold"))
        Password.grid(row=3, column=3,columnspan=2)
#............        
        Username_key = tk.Entry(self, textvariable = user_key, width=19, font=("Helvetica", "15"))
        Username_key.grid(row=2, column=5,columnspan=5)
        Password_key = tk.Entry(self, textvariable = psw_key, width=19, font=("Helvetica", "15"))
        Password_key.grid(row=3, column=5,columnspan=5)
        log_in = tk.Button(self, width=7, text="Log In", command=lambda: controller.show_frame("StorageOrMotor"))
        log_in.grid(row=5,column=8,columnspan=2)
#............`I try to create a clear button`
        Clear = tk.Button(self, width=7, text=" Clear " ,command=lambda:clear_message())
        Clear.grid(row=5,column=5,columnspan=2)

Answer 1

clear_message()属于MainPage类，因此在该类中调用它时，需要使用self.前缀。此外，定义方法时需要使用 self 作为参数，因为它是类的成员。

def clear_message(self): #self here
    user_key.delete(0, 'END')
    psw_key.delete(0, 'END')

此外，由于clear_message不接受任何参数，因此您不需要在那里使用 lambda 表达式。

#self here and removed lambda
Clear = tk.Button(self, width=7, text=" Clear " ,command=self.clear_message)