python response slow when running external DLL

[Peter Otten]

jfong at ms4.hinet.net wrote:

> Peter Otten at 2015/11/27  UTC+8 5:19:17 PM wrote：
> 
> Hi! Peter, thanks for your prompt reply.
> 
>> What does var_status.set() do? If it writes to stdout you may just need
>> to flush().
> 
>    var_status is a StringVar which binds to a lable's textvariable. I use
>    this label as the status bar to show message.

Can I conclude from the above that you are using tkinter? Widgets can only 
update when the event loop gets a chance to run. While a quick fix is to 
invoke update_idletasks() callbacks shouldn't generally contain long-running 
code that -- as you have seen -- will block the complete user interface.
 
>> Do you see the same behaviour when you replace mydll.SayHello() with
>> something simple like time.sleep(1)?
> 
>     I use time.sleep(3) to replace mydll.SayHello(), still get the same.
> 
>> As a general remark keep your test scripts as simple as possible.
>> Example: If
>> 
>> import mydll
>> print("Download...", end="")
>> mydll.SayHello()
>> print("OK")
>> 
>> showed the same behaviour it would be the ideal test script.
> 
>     I run the above statements in a test file, it works as expected. I can
>     see "Download..." and then "OK".
> 
> 

Quick-fix example:

#!/usr/bin/env python3
import tkinter as tk
import time

def download():
    var.set("Starting download...")
    root.update_idletasks()
    time.sleep(3)
    var.set("... done")


root = tk.Tk()
var = tk.StringVar()
label = tk.Label(root, textvariable=var)
label.pack()
button = tk.Button(root, text="Download", command=download)
button.pack()

root.mainloop()

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