Tkinter grid and time.sleep() - time

Question

I would like a label to be .grid() then the program to wait 3 seconds and then .grid_forget(). I am very confused at the point .grid is executed. For example:
def remove_choice(self):
while True:
try:
get = int(self.entry_remove_choice.get())
except ValueError:
self.label_error_remove.grid(row=10,column=6) #A
time.sleep(3)
self.label_error_remove.grid_forget() #B
#Empty entry box
break
else:
#continue code
break
Once the button is pressed and remove_choice is executed, the button is displayed to be pressed in for three seconds then #A and #B are executed in one go and nothing is displayed.
If #B is removed then the error message is displayed after three seconds.
If #A and #B are swapped for print to terminal then program works how you would think, with one message, a wait of three seconds, then another message.
If you do a very sloppy solution (which Im not that bothered about for this program) and do this:
def remove_choice(self):
while True:
try:
get = int(self.entry_remove_choice.get())
except ValueError:
self.label_error_remove.grid(row=10,column=6) #A
for n in range (1,1000):
print("abc")
self.label_error_remove.grid_forget()
break
else:
#continue code
break
When executed "abc" is printed 1000 times taking around 1.5 seconds and then after this the program displays the grid.
Any suggestions to how to make TKinter wait please.
Also can someone explain why grid works like this, thanks.

Answer 1

Rather than trying 'forgetting' the label each time, why not just clear the error message text?
My example below will wait for the user to press the button and display the error message for 3 seconds. I'm using the .after method to schedule the hideError method 3 seconds (3000 ms) after the error message is displayed.
try:
import tkinter as tk
except:
import Tkinter as tk
import time
class App(tk.Frame):
def __init__(self,master=None,**kw):
tk.Frame.__init__(self,master=master,**kw)
self.errorMessage = tk.StringVar()
self.ErrorLabel = tk.Label(textvar=self.errorMessage)
self.ErrorLabel.grid()
self.button = tk.Button(text="Press Me",command=self.showError)
self.button.grid()
def showError(self):
# Disable the button and show the error message
self.button['state'] = tk.DISABLED
self.errorMessage.set("Error Message!!!!")
self.after(3000,self.hideError)
def hideError(self):
#Enable the button and clear the error message.
self.button['state'] = tk.NORMAL
self.errorMessage.set("")
if __name__ == '__main__':
root = tk.Tk()
App(root).grid()
root.mainloop()
It is considered bad practice to use while True loops or time.sleep inside GUI applications. They prevent the GUI from updating so in your code both actions appear to happen at the same time because the time.sleep operation is blocking the GUI and preventing the screen from being redrawn.
EDIT: Passing arguments from callbacks.
Current problem is that the after method expects to receive a reference to a function. self.hideError(3) returns NoneType not reference to a function call. We can solve this using anonymous functions and lambda.
I've started to use this snippet of code to help, its from guizero
def with_args( func_name, *args):
"""Helper function to make lambda functions easier
Thanks to guizero"""
return lambda: func_name(*args)
Then in your main section of code the line would look like this.
self.after(3000,with_args(self.hideError,3))
EDIT: There is an even simpler way. The .after method can take arguments itself.
self.after(3000,self.hideError,3)