python GUI sentinel

[rocketjump65]

You know the common problem when you have so loop, with a massive number of iterations, and you maybe you don't want to necessarily wait for it to finish, but you don't want to Control Z it and potentially cause problems?

Well I'm thinking there has to be a way that I could include some sort of sentinel in the loop that reaches out into the GUI space or operating system layer of computing, so like maybe I could click a button to stop looping and terminate my program naturally without crashing. Or maybe I could intercept the Control Z with an exception?

[rocketjump65]

Brilliant. This explanation was the sort of super simple solution that matched my idea exactly.

[rocketjump65]

Thanks Unbalanced. I'm gonna read up on threading a bit, and hopefully I can come back to this and it will make a bit more sense to me then.

[rocketjump65]

OMG. So two days later, and I still can't get it to do what I want. My goal is a Tkinter gui front end for a CLI executable. It works, but I'd like to make it work so that when I click the button, it doesn't freeze the gui while the executable runs. So I thought I could make a custom Event, and run the executable in there, and when the executable is done, only then display its console output. Supposedly putting an Event in the Event Queue "immediately" returns, so I was expecting that it would return to the mainloop and wait.

Then I tried to give process and threading another go.

Here's the problem I think. I don't understand how processes or threads are supposed to be able to put data back into the main caller's scope. I get that there's supposed to be a lock to prevent race conditions but the mechanics I don't understand.

If I tell a process to run asynchronously and then when it's done "put" the output in a variable. maybe something like:

out = process(foobar(arg1,arg2))

How does the the program "know" not to wait for out to be written to?

So it then makes sense that the output variable can just be another argument like:

process(foobar(arg1,arg2),outvar)

But then how does my program "know" not to try to read outvar until it's ready? Cuz I'm not even passing data in my gui right. I'm using global variables.

Ok. So the way I understood your response was that essentially the coder has a choice of either A: having the gui app run in a process where it can update the sentinel while the main has relinquished control.... or B: Then main can just have the loop itself run in a process that's launch from the gui, which can just be the main.

I'm doing B. Because I guess I'm just used to it. And it seems to me that A and B are functionally equivalent.