Python tkinter, how to display the message one by one - python-3.x

Question

I'm using tkinter (Python version 3.9) to build an application. In the application, I want the message can be shown one by one according to the progress of the program. However, my application now can only print all the messages together.
The example code is listed as below:
import time
import tkinter as tk
def start():
txt_edit.delete(1.0, tk.END)
for _ in range(10):
txt_edit.insert(tk.END, f"\nmessage should be printed out one by one")
# do something here
time.sleep(0.5)
# job done
window = tk.Tk()
window.title("User Interface")
window.rowconfigure(0, minsize=40, weight=1)
window.rowconfigure(1, minsize=200, weight=1)
window.columnconfigure(1, minsize=200, weight=1)
lbl_1 = tk.Label(master=window, text="Question: ")
lbl_2 = tk.Label(
master=window, text="How to print the text out one by one?", anchor="w"
)
lbl_1.grid(row=0, column=0, sticky="ns")
lbl_2.grid(row=0, column=1, sticky="nsew")
txt_edit = tk.Text(window, relief=tk.SUNKEN, bd=2)
fr_buttons = tk.Frame(window)
btn_open = tk.Button(master=fr_buttons, text="Start", command=start)
btn_open.grid(row=0, column=0, sticky="ew", padx=5, pady=5)
fr_buttons.grid(row=1, column=0, sticky="ns")
txt_edit.grid(row=1, column=1, sticky="nsew")
window.mainloop()
What is the solution to this problem? Thanks!

Answer 1

Calling time.sleep() from tkinter applications isn't a good idea. Your mainloop and time.sleep() are conflicting. Your program works fine, but the changes are not displayed.
The easiest solution is updating the screen. But as I said, you should avoid using time.sleep(). The following solution satisfies your question, though it freezes your program and will not work on a larger application.
def start():
global window
txt_edit.delete(1.0, tk.END)
for _ in range(10):
txt_edit.insert(tk.END, f"\nmessage should be printed out one by one")
# do something here
time.sleep(0.5)
window.update() # show changes
# job done
I would recommend dropping the time module. You can use a timer instead. Also, take into account the while loop. You might want to use multi-threading inside your applications. Here's a simple Timer object and implementation:
class Timer:
# --- Timer object ---
def __init__(self):
self.start_time = None
self.on = False
def start(self):
# start counting
self.start_time = time.time()
self.on = True
def value(self):
# --- return current value ---
if self.on:
return time.time() - self.start_time
else:
return 0
def stop(self):
# --- stop counting ---
self.__init__()
def start():
txt_edit.delete(1.0, tk.END)
msg_count = 0
timer = Timer()
timer.start()
while msg_count != 10:
window.update()
if timer.value() > 0.5:
txt_edit.insert(tk.END, f"\nmessage should be printed out one by one")
timer.start()
msg_count += 1
timer.stop()