How to show “Loading…” and then run script after clicking button in tkinter?

Question

I want to show "Loading..." and then execute a script while the user waits.

I understand that the canvas can only update itself after every loop, and that while the button command is called the canvas is frozen.

How could I fix this?

Currently, there is no text that appears. The success text does appear.

import tkinter as tk
import main


root = tk.Tk()  # create GUI instance
root.title('Exam Closeout')  # name GUI

def run_script():
    '''
    Run the script from main, that is, the data script.

    :return: void
    '''
    # show loading status: currently doesn't work, need to understand queue better
    current_text = tk.StringVar()
    current_text.set('Loading...')
    tk.Label(root, textvariable=current_text).grid(row=4, column=1, sticky='w')
    subject = entry_1.get() # grab subject from user input
    try:
        # call main
        main.test(subject)
        # show finish status
        current_text.set('Script successfully finished. You may exit out of this window now')
    except Exception as e:   # catch exceptions. currently doesn't show specific exception
        current_text.set("Error occurred. Try looking at documentation")


# label with instructions
tk.Label(root, text="Thank you for using me...").grid(row=1, column=1, sticky='w')

# label to show users where to enter exam
tk.Label(root, text="Enter exam code:").grid(row=2, column=1, sticky='w')

# blank box to enter exam into
entry_1 = tk.Entry(root,width=40)   # entry has to be its own line - for more, see below
entry_1.grid(row=2, column=2, columnspan=2)

# button to run script
tk.Button(root,text="Run", command=run_script).grid(row=3, column=3)

# start canvas
root.mainloop()

main.py

import time

def test(exam):
    time.sleep(5)
    print(exam)

In case it matters, main method is actually a data analysis script that takes in dataframes, manipulates them, and exports an Excel dataset.

Answer 1

Add a call to the universal update_idletasks() widget method at the location indicated below:

def run_script():
    '''
    Run the script from main, that is, the data script.

    :return: void
    '''
    # Show loading status.
    current_text = tk.StringVar()
    current_text.set('Loading...')
    tk.Label(root, textvariable=current_text).grid(row=4, column=1, sticky='w')
    subject = entry_1.get() # grab subject from user input
    try:
        root.update_idletasks()  #### ADD THIS LINE ####
        # call main
        main.test(subject)
        # show finish status
        current_text.set('Script successfully finished. '
                         'You may exit out of this window now')
    except Exception as e:  # Catch exceptions.
        current_text.set("Error occurred. Try looking at documentation")