销毁方法的属性错误

Question

I am getting the following error,if i click the button when the Entry box has kept empty. It runs without errors once i enter the values and click but not when leaving the entrybox empty and clicking

Error:

Exception in Tkinter callback
Traceback (most recent call last):
  File "C:\Python27\lib\lib-tk\Tkinter.py", line 1470, in __call__
    return self.func(*args)
  File "C:/Python27/tew.py", line 31, in retrieve_inpu
    self.label.destroy()
AttributeError: 'NoneType' object has no attribute 'destroy'

Coding:

import Tkinter as tki
import MySQLdb
db = MySQLdb.connect(host="localhost", # your host, usually localhost
                         user="root", # your username
                          passwd="mysql", # your password
                          db="sakila") # name of the data base
cursor = db.cursor()

class App(object):
     def __init__(self,root):
         self.root = root

         self.txt_frm = tki.Frame(self.root, width=900, height=900)
         self.txt_frm.pack(fill="both", expand=True)
         button3 = tki.Button(self.txt_frm,text="CLICK 1", command = self.retrieve_inpu)
         button3.grid(column=0,row=2)
         self.entry = tki.Entry(self.txt_frm)
         self.entry.grid(column=1,row=0)

         #place holder for label variable
         self.label = None
         self.label1=None

     def retrieve_inpu(self):
        ent = self.entry.get()


        cursor.execute('SELECT A1,A2,A3 FROM adarsh1 WHERE A1=%s', (ent,))
        row = cursor.fetchone()
        if row is None:
           self.label.destroy()
           self.label1.destroy()
           #or self.label['text'] = ''
           return
        #destroy the widget if it has been created
        #you will have a bunch of orphans if you don't
        if self.label:
            self.label.destroy()

        self.label = tki.Label(self.txt_frm,text=row[1])
        self.label.grid(column=0,row=3)

        if self.label1:
            self.label1.destroy()

        self.label1 = tki.Label(self.txt_frm,text=row[2])
        self.label1.grid(column=0,row=4)            



root = tki.Tk()
app = App(root)
root.mainloop()

Answer 1

Read the error:

    self.label.destroy()
AttributeError: 'NoneType' object has no attribute 'destroy'

This means that self.label is None , so you can't destroy it. You could fix this by doing the same thing as you do later in the code, and checking if it is None before you destroy it:

if row is None:
    if self.label:
        self.label.destroy()
    if self.label1:
        self.label1.destroy()
    #or self.label['text'] = ''
    return