Make your Python Code More Readable with Custom Exceptions

Key Takeaways

hey guys it's Daniel with another quick python tip for you so today I want to talk about how you can make your code more readable using custom exceptions um so to give you an example when you might want to do that uh let's say we have a simple function here we're going to call it validate and we're going to pass it a name which is just a simple string variable and that function is going to do a simple check on um name just to see if um if it's less than 10 characters long right and if it's less than 10 characters long we want to reject that name because we're just going to say hey you know what it's not a valid name so uh one way to communicate that to um someone who might be calling that function you know one of your co-workers um maybe you're going to call that function yourself somewhere in the code I mean it's highly likely considering that we're writing the function um what's the best way to communicate that right sure we could just return none H it's kind of easy to miss and just ignore that so typically what you do is you'd raise an exception um and we would probably pick something like uh Python's built-in value error right and um so what would happen now is that when we take this function and we call it on a name that's less than 10 characters wrong uh long we get a value error so let's take a look at what that looks like so let's define validate here and we're just going to call validate on uh a three character name here and we get the Val ER value error right that's sort of the error report that we would get in in a trace back uh when our program crashes um that's okay you could probably use that to trace it back to the line you were working in you could kind of figure out why you got that value error maybe um a way to to make that a little bit more clear and just to communicate the intent a little better would be to say okay we're going to do a value error and uh we're going to tell you that the name is too short so if you do that what happens is um that you get a little bit of more context right we're going to tell you hey the name is too short so the downside of that is um programmatically it becomes really difficult to distinguish between you know a name too short kind of value error and just any other old value ER so that's not great but there's a really good way to fix this that I'm going to show you now so what you would do in this case is you would create a new um subass of value error and we're going to call that um name to short error and that's going to be based on the original value error and because we're not you know we're not even trying to add more stuff to Value error we're not going to add extra for behaviors or properties so we're just going to say pass here to leave the class alone but what we've done now we've created a new type that we can now actually use in um our code here and um what's cool about this now is that when we when someone runs this code and they actually trigger the condition that raises the value error they will get a name to short error right you get that initial console because I'm running this in inside the Python 3 interpreter here but um it gives someone who hits that error a bit more context um and tells them the the original programmer's intent right you're going to be able to quickly figure out oh okay you know this is being triggered because the name was too short and we can make this a little nicer still so what I like to do in uh in a situation like this is to actually pass the uh value that cost the error to um my custom exception type right so um in this case we would obviously pass name and then when we run this in the python reppel you will see that uh the error report is kind of nice at this point because you know if this blows up this is what you would see eventually in your in your uh Trace back when when you get uh the the the exception printed out at some point um you would see something like that name to short error Joe um and that was cost invalidate so at this point it would be really easy for someone else or maybe your your future self to identify what went wrong here and um you're probably going to save yourself more time then the time it you know then the time it took you to to go and Define that custom exception type so as with all things you know it's not something you should overdo but it can be extremely helpful especially if you're defining um a public API for for um let's say a module that you want to share with other people um that sort of stuff is going to save you tons of time and it's just going to make you a lot more productive as a developer cool I hope this helped you out uh take care and write more python