Peter Otten at 2015/11/27 UTC+8 8:20:54PM wrote:

> Quick-fix example:
> def download():
>     var.set("Starting download...")
>     root.update_idletasks()
>     time.sleep(3)
>     var.set("... done")

Thanks, Peter, The update_idletasks() works. In my trivial program it's easy to 
apply for there are only two places call the DLL function.

> A cleaner solution can indeed involve threads; you might adapt the approach 
> from <http://effbot.org/zone/tkinter-threads.htm> (Python 2 code).

Using thread is obviously more logical. I think my mistake was the "while busy: 
 pass" loop which makes no sense because it blocks the main thread, just as the 
time.sleep() does. That's why in your link (and Laura's too) the widget.after() 
scheduling was used for this purpose.

From what I had learned here, the other way I can do is making the codes 
modified as follows. It will get ride of the "result" and "busy" global 
variables, but it also makes the codes looks a little ugly. I think I will take 
the update_idletasks() way in this porting for it seems more simpler, and can 
be used on thread or non-thread calling. Thank you again.
    .....
    .....
    #do the rest
    var_status.set('Download...')
    _thread.start_new_thread(td_download, ())  #must use threading

def td_download():
    result = mydll.SayHello()
    if result:
        var_status.set("Download Fail at %s" % hex(result))
        showerror('Romter', 'Download Fail')
    else:
        var_status.set('Download OK')            
        showinfo('Romter', 'Download OK')

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