Python 3 Programming Tutorial - Tkinter event handling

Key Takeaways

Hello way and welcome to part three of our tkinter tutorial series in Python 3. Where we left off, uh we made our window. Um and in fact, we can just go ahead and pop it up. Made our window here. Uh simple guey window. We can resize it. We can close it. We can click on this button, but we can't it's not doing anything. So we want to have some sort of event handling ability. So close this. And what we're going to want to do here is we say button. We give it you know self which could be bajumba text equals quit but then there's another parameter here that we can add in and we can say command and basically what command is is what do we want to happen right when we when someone clicks on this button when this button is like uh activated what do we want to happen well what we might want to happen is the following so self dot and then we're going to call it client_exit okay now client exit actually has no um doesn't exist yet. So that's not something that's you know built into tkinter or anything like that. So we define client exit. So it could have been called really anything we wanted. So now what we're going to do is same you know in our oops in our window class here um min class we have you know all these functions and stuff. So now what we can do is we can come down here and we can define a new function. Now uh this function we'll say define client_exit and then we'll say self and uh we'll just leave the parameters for now. And just as a quick aside um I've been getting some comments on one of my other series entirely and uh the the comment was that we're referencing functions before they've been defined. And so some people have been having trouble because they're trying to reference. They're it's like throwing an error saying, you know, this hasn't been defined yet and you're trying to reference it. Uh, and so they're saying that in the in the code it was for it's for a Pygame tutorial series and in the code it's basically something like this where we're referencing self.clientexit before we're actually at self or we're at client exit, right? So we're referencing this function before it even exists. And then we did it again up here, right? and we kept doing it. That's not against the rules of Python because right here we're just defining functions. And so functions are kind of like load you don't envision, you know, functions aren't really loaded until maybe the very end or it's it's hard for me to explain how why this is okay. It's basically acceptable because a definition of a function is not a running. So when you define a function, it's not being run. It's just being defined. And so when it really matters is when you call the function to be executed, it's going to say, okay, it's going as we load this function in, it's going to, you know, tell P or Python's going to be built like, okay, so we've got this quit button. It's a button. When it's clicked, we need to reference client exit, but it's not trying to reference client exit right at that moment. It's it's just storing to memory like what does it need to do with that function. So right now, putting self.clientexit client exit before the function client.exit. That's totally fine. That's not actually we're not reference I mean we are sort of you know in theory referencing it before it's been defined but we're not actually calling it before it's been defined. We're just storing it to memory. So a little bit different there. So if at the same time if like above class window let's say we called uh you know window um init window like that. Okay. Okay, if we did something like that, then yes, we would be defying um the principles because we we're calling first of all class window before it's been defined, but also init window before it's been defined. We're calling it to execution and we can't. So, just as a quick aside, not really quick, but um needed to be covered because like I said, some people were getting really confused about that in the Pi game tutorial series and maybe some people are getting confused about it now. Python is a scripting language, so it will go line by line, but it's only going to execute something that you're asking it to execute. So, um anyway, moving along. So, client x itself um actually can be very basic. We can say client exit self uh and all we really need to do is just exit. Okay, so we can call just this exit function. It's a built-in uh function into Python. So, with that, uh we can do this. And so, again, quit button. It's a button. It text says quit. Uh, and the command for it is self.client_exit. So when we click on the button, it's going to run that function. So it comes down here. It says client exit. What do we do? Exit. Done. So we can save that and we can run it. And up pops our guey. And we can hit quit. And just for the record, this pops up. The program is still running. Do you sure you want to kill it? We do. So we'll hit okay. And that's that's fine. Okay. So that is um some button or some error handling. Will you go away? That is um not error handling event handling uh with tkinter. Obviously we can make this much more complex. So in this sense all the button did was run client exit and all client exit did was exit. Now you can kind of foresee in the future some of these buttons might do some more fancy things than just that. Um but that's basically how you you would handle it. Okay. So, if anybody has any questions or comments regarding this video as as far as uh maybe what I was talking, you can also talk about uh referencing it before it's been defined if you if you're still confused about that. But if anybody else has any questions about whatever, uh feel free to leave those below. As always, thanks for watching. Thanks for all the support and the subscriptions. And until next time.