Python Programming Tutorial #18 - Try and Except (Python Error Handling)

Key Takeaways

hey guys welcome back to another video this is the eighteenth video in my Python programming series and today we're going to be talking about something called a try and accept block of code so just like we talked about the if-else and Elif block of code and like we talked about the for loop which is a block of code and like functions which are blocks of code we're gonna be talking about to try and accept so in Python we use try and accept as our keywords and other languages you may have heard of try and catch statements this is the same thing except in Python instead of catch we use accept okay so let's talk about what a try and accept statement is sometimes in Python you want to do an operation or you want to try something but you don't know if it's really going to work or not there's some different variables they may come in sometimes it may work sometimes it may not work usually this depends on user input or what the user is doing in the program so a good example of this is maybe if we're validating a form so we'll do an example you would say text is equal to input like this and then we'll say username okay now in typical user names you're only allowed certain characters maybe you can't do a comma you couldn't do a star certain things like that right maybe we only want it to be text so we only want it to be numbers we just want to validate this we could use a huge if statement to do this but instead there's something called a try and except that we can use so in this case I want my username to only be numbers so I don't want it to be string at all I want it to only be numbers so what I'm going to do is I'm going to make a new variable here and I'm going to call it number and all I'm going to do is I'm going to try to int the text like this okay so if you remember what the int does is that simply converts our string into an integer and then I'm going to print that to the screen so I'm going to print number to the screen now what happens right here is if I try to type in a word like this you see we get an error it says there's an invalid literal for inks with base 10 now you don't have to understand what this error is pretty much all this means that we can't convert too low into a number because there is really no number there how how does it know what number to make that into right so in this case we would use a try and except look because if the user types in something that's invalid well we want them to type in something else we don't want the program to crash like it just did there so here I'm going to put a try like this followed by a colon and then I'm going to indent these two blocks right here so that means we're going to try this block of code okay and then underneath here I'm going to type except just like that followed by a colon now there is a more advanced way to do this we can accept a specific type of error but I'm not going to talk about that in this video this is just a very basic try and accept block and then under here I'm going to type what I want to happen if this block of code doesn't run meaning this block of code returns an error and we can't actually execute it so in this case I'm just going to do I'll just print to the screen invalid username because remember we're only going to have our username contain numbers all right so now if I run the program and I try to type in something that is not a string so just I mean that is not a number like this it will just say invalid username rather than crashing the program which is what happened before and if I do try to type in something that is valid so maybe I type one two three four it just gives me that username back right so it works like that um so that's pretty much how we try and accept works again this is a very basic example that's what I try to do in my videos just give you the basics and then you can try to apply it to some projects you're doing and some more advanced things so again what happens is it tries this block of code if that block of code doesn't run or an error happens instead of simply crashing the program and giving us that red message it's going to go to this except block and it's going to do whatever's in here now in this except block again we could ask them to type in a new username we display another message we could maybe close the program on them we could do whatever we want to do in this accept block and it's extremely useful so yeah that's pretty much how the try and accept works if you've learned something please like and subscribe and I will see you again in another video