使用 tkinter 刷新，文本输出缓慢

Question

i was wondering if it would be possible to output text slowly using tkinter and a label

the main problem is I don't know how to get it to flush. I press the button, and then it waits 9 seconds, then it prints the whole thing.

How do i get this to work with a flush i've tried label1.flush(), but it gives me an error also sys.stdout.flush() does't work, but it makes sense because this is to the console

def clicked():
    txt = "hello world"
    a = txt[0]
    label1 = tk.Label(window,text=a)
    label1.place(x=60,y=30)
    time.sleep(9)
    b = txt[1]
    c = a+b
    label1 = tk.Label(window,text=c)
    label1.place(x=60,y=30)

Answer 1

You should not use time.sleep with tkinter as it blocks the GUI processing. This causes it to print the whole thing in one go. Flushing is not possible because this is a Tkinter GUI, not a console, so there is no stdout to flush. Instead, you have to do something like this:

import tkinter as tk

def clicked():
    n = 0
    txt = "hello world"
    showChar(n, txt)

def showChar(n, txt):
    n += 1
    label.config(text = txt[:n])
    if n < len(txt):
        root.after(9000, lambda: showChar(n, txt))

root = tk.Tk()
label = tk.Label(root, text = "")
label.pack()
button = tk.Button(root, text = "Start", command = clicked)
button.pack()
root.mainloop()

When the button is clicked, the counter is initialised (set to 0) and the text is set. Then showChar is called. This function increments the counter, then updates the label text to show an extra character. If the string hasn't been full displayed yet, it waits 9000ms (or 9 seconds) until it runs itself again, using the tkinter method root.after . This then works as you want it to.

Answer 2

Here is a way to do this using .after loops:

from tkinter import Tk, Label


def print_slow(widget: Label, text, delay: 'in miliseconds', index=1, start_index=0):
    widget.config(text=text[start_index: index])
    index += 1
    return root.after(delay, print_slow, widget, text, delay, index) if index <= len(text) else None


root = Tk()

label = Label(root, text='')
label.pack()

print_slow(label, 'hello world', 2000)

root.mainloop()

So pretty simple:
First import only what You need, don't use wildcard ( * )

Second define the function, it will take arguments such as the widget to which it is needed to print slowly, then the text that has to be printed, then delay in milliseconds between characters appearing on the screen, then the end index and start index.

Then simple tkinter stuff:
.config() the widget's text attribute to the text from start_index to the end index
Then increment the end index by one
Then use .after() to schedule the same function (loop) after the given delay and pass the incremented index argument

Then the simple tkinter stuff and also remember to initially call the function

EDIT: updated the function to actually stop when finished, used some ternary conditions to return None (basically stop in this case) if the index is bigger than the lenght of the text