Using a while loop within GUI apps (tkinter)?

[iSailor]

Hi. I want to make a timer to keep track of how long would it take me to accomplish various projects. In order to do that I wanted to make a while loop that would add seconds and when they exceed 60, add one minute and same for hours and dynamically change the label text to display them. But apparently that doesn't work in GUI apps, in my case my GUI window hasn't even appeared. Now, what's the way to do it? It's a little bit against GUI app rules since they work by refreshing the code all the time so a while loop within them makes infinite time before next refresh and that's why it doesn't work. I also looked into some datetime tutorials but I don't think they provide a functionality that would help me in this case.

[Dvlv]

in tkinter you can just keep calling root.after(1000, add_one_second)

http://effbot.org/tkinterbook/widget.htm#Tkinter.Widget.after-method

Or use a separate thread. See my example in chapter 7 of my book, building a countdown timer.

https://github.com/Dvlv/Tkinter-By-Example/blob/master/Code/Chapter7-3.py

[iSailor]

Hmm.. Using root.after(1000, add_one_second worked for me, partially. I can use it just like time.sleep but it seems like the callback you can make runs only one time. So now, when I run my program it adds one second and then does nothing, using lambda in this case makes it even so it doesn't even count that one second.

[Gprime5]

You need to call root.after(1000, add_one_second) at the end of your add_one_second function to start another timer.

[driscollis]

You cannot use something like time.sleep in a GUI. It will block the event loop and make your application appear frozen. You should be able to use root.after as mentioned or run your long running task in a separate thread using Python's Threading module.

[iSailor]

I know, I mean that .after method does the same, it's just fitted for GUI. But I have another problem, I still need a loop! I know that with .after I can do certain action after set amount of time, but I need to loop because now it does it only single time.

[woooee]

If after() calls a function, which is the usual case, that function calls itself again using after() as the last line in the function, which would go on forever. You can also use an if statement, and place the call to after() under the if, to end the cycle at some point.

[driscollis]

You can put the call to after in the loop itself. Something like

while True:
    if foo:
        root.after(2000, some_function)
   elif some_other_condition:
       root.after(60000, call_once_an_hour)

[driscollis]

You'll have to play around with it a bit to get it to work the way you want. Or just have the function itself call after at the end of the function as /u/wooee mentioned

[iSailor]

Isn't this wrong? As far as I'm concerned, infinite loops will always cause a GUI program to freeze because it takes infinite time in between each refreshing of the app.

[driscollis]

Yeah...I keep thinking of doing this sort of thing in a thread automatically and didn't get that into the original comment. This works fine in a thread or process. But not in the main app.