Tkinter 标签小部件中的动画文本（python）

Question

i want to animate a label text in tkinter (python). for that purpose, i am using time.sleep() method for updating 1 character in Label widget after a second but it is not updating Label widget instantly rather it is updating label at once at the end of timer. How could i fix this?. Here is my code:-

from tkinter import *
import time


global a



def update(a):
    txt = 'Sample Text'
    mylabel.configure(text=txt[0:a])
    
def timer():
    global a
    a = 0
    lenth = len('Sample Text')
    start = time.time()
    while True:
        # Do other stuff, it won't be blocked
        time.sleep(0.1)

        # When 1 sec or more has elapsed...
        if time.time() - start > 1:
            start = time.time()
            a = a + 1

            # This will be updated once per second
            print("{} counter".format(a))
            update(a)
            # Count up to the lenth of text, ending loop
            if a > lenth:
                break

root = Tk()
root.geometry('300x300')

mylabel = Label(root, text="S", font=('Bell', 36, 'bold'))
mylabel.pack(pady=5)

root.after(3000, timer)
root.mainloop()

Answer 1

It is not recommended to use loop and time.sleep() in the main thread of a tkinter application because it will block the tkinter mainloop() from updating widgets until the loop exits. That is why you can only see the result after the loop completes.

Use .after() instead:

import tkinter as tk

root = tk.Tk()
#root.geometry('300x300')

txt = 'Sample Text'

lbl = tk.Label(root, font='Bell 36 bold', width=len(txt))
lbl.pack(pady=5)

def animate_label(text, n=0):
    if n < len(text)-1:
        # not complete yet, schedule next run one second later
        lbl.after(1000, animate_label, text, n+1)
    # update the text of the label
    lbl['text'] = text[:n+1]

# start the "after loop" one second later
root.after(1000, animate_label, txt)
root.mainloop()