我在销毁按钮时收到错误 _tkinter.TclError: bad window path name “.!button”

Question

from tkinter import *
master=Tk()
class check:
def __init__(self,root):
    self.root=root

    self.b1=Button(root,text="Click me",command=self.undo)
    self.b2=Button(root,text="Again",command=self.click)

def click(self):
    self.b1.place(relx=0.5,rely=0.5)

def undo(self):
    self.b1.destroy()
    self.b2.place(relx=0.2,rely=0.2)
c=check(master)
c.click() 
master.mainloop()

This is my code. I get _tkinter.TclError: bad window path name ".!button" error only when I use destroy method. But I want to delete previous button when another button appears.What should I do?

Answer 1

What are you doing? When you click the "Click me" button (and call the self.undo method, where the self.b1 button is destroyed) and then click the "Again" button (and call the self.click method, which tries to place already destroyed self.b1 button), you get the error, that the button does not exist. Of course, it doesn't because you have destroyed it.

It looks like you meant to hide the button. If you intended to do this, then you could just use .place_forget() method (there are also .pack_forget() and .grid_forget() methods for pack and grid window managers, respectively), that hides the widget, but not destroys it, and hence you would be able to restore it again when you need.

Here is your fixed code:

from tkinter import *


master = Tk()

class check:
    def __init__(self, root):
        self.root = root

        self.b1 = Button(root, text="Click me", command=self.undo)
        self.b2 = Button(root, text="Again", command=self.click)

    def click(self):
        self.b2.place_forget()
        self.b1.place(relx=0.5, rely=0.5)

    def undo(self):
        self.b1.place_forget()
        self.b2.place(relx=0.2, rely=0.2)

c = check(master)
c.click() 
master.mainloop()

I can also give you a piece of advice about the implementation:

1) You should write the code according to the PEP8 style ; classes should be named in the CamelCase .

2) You should inherit your Tkinter app class(es) either from Tk (usage is shown below) Toplevel(the same as Tk, but use ONLY for child windows), Frame class (almost the same as for Tk, but you need to pack/grid/place that Frame in a window).

3) It's better to create the widgets in a separate function (it helps while developing complex and big apps).

4) It's recommended to write if __name__ == "__main__": condition before creating the window (if you do like this, you will be able to import this code from other modules, and the window won't open in that case).

Here is an example:

from tkinter import *


class Check(Tk):
    def __init__(self):
        super().__init__()

        self.create_widgets()
        self.click()

    def create_widgets(self):
        self.b1 = Button(self, text="Click me", command=self.undo)
        self.b2 = Button(self, text="Again", command=self.click)

    def click(self):
        self.b2.place_forget()
        self.b1.place(relx=0.5, rely=0.5)

    def undo(self):
        self.b1.place_forget()
        self.b2.place(relx=0.2, rely=0.2)

if __name__ == "__main__":
    Check().mainloop()

Answer 2

After you destroyed button b1 in the undo(self) function tkinter cannot access it anymore and will be confused when you try to place is somewhere in the click(self) function.
To make button b1 only disappear visually you could place it outside of the window instead of destroying it.
To do so replace

self.b1.destroy()

with

self.b1.place(relx=-5, rely=0)

This will move the button b1 far to the left, where it cannot be seen.
When calling the click(self) function, the button will reappear, because it will be moved inside the window again.