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Instructor: Let's try a different example here.

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Let's say I'm creating a simple sum function.

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Yes I know it already exists in Python

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but we'll just create our own.

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A simple one that takes num1 and num2

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and in here we'll just return num1 plus num2.

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Now if we were to just simply do sum1

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and sum2 and I ran our program.

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Well let's print it out first.

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I click run.

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I get one and two

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because it just adds the two strings together.

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So let's just do this

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and click run.

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I get a type error.

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Must be a string not INT.

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So based on what we learned

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how do we handle this?

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Well we can add a try block in here and wrap this function

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or we can build it directly into our function.

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So I can say try.

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This part and here have an except clause

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that says perhaps if we get a

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any type of error we'll print something is wrong.

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If I run this.

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I get something is wrong.

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But here's a problem.

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By just doing except with no exceptions.

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As a programmer, I'm reading this

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and I don't really know what actually went wrong.

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Because it could be so many things.

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So a good practice is to always catch these errors based

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on a specific exception.

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This way you know what the error is

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and you can be more descriptive.

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So here we can say type error.

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And this type error we can just say please enter numbers

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so that if I run this I get please enter numbers.

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So now, alright, my error is more descriptive.

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I should fix this and make sure that I enter numbers.

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Awesome.

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Now a common pattern when doing error handling

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is to do something like this.

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Type error as

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and then doing something like a variable.

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So whatever variable we want.

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In our case, let's just say error.

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So I'm saying, hey, if you catch type error

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let us use error in our error message.

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So I can say here

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plus error.

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So that if I run and let's do a string here.

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If I run.

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Look at that.

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I get the error printed.

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Let me just open this up a little bit

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so you can see it clear.

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Look at that.

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It actually gives me the error that I want.

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So that I can see that on line five.

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On this line I get a type error.

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Unsupported operant.

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And I get a descriptive error of what is happening.

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So maybe I could use it in my output message.

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But what if I don't want to use this?

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And I do run?

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All right, everything is working.

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Again, if I do plus error and I click run.

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And this is actually tricky

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but it says here during handling of the above exception,

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which I'm doing, another exception occurred.

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Oh boy.

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I try to handle something

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and I had an error within that error.

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So this is sometimes tricky

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but what it means is what we get

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out here is actually an error object.

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It's a built in exception in Python.

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You can't add in here the way I have.

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Instead we wanna use an F string.

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So I do F and then here pass it the error.

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So that now

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if I run this

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I get please enter number.

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Unsupported operant type S for plus INT and STR.

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So I actually get this error available to me.

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Now if I was to just print this error

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let's see what it looks like.

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If I click run.

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You see this is the part of the error that we get.

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So it's very, very useful

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if you wanna give meaningful errors to your users.

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Another interesting thing you can do

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is something like this where you wrap these errors together.

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So let's say we have zero division error as well.

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And here we'll just say, oops.

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If we, for example, divide num1 by num2.

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Let's just run this first.

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I get, oops.

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If I do one divided by zero

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and I run this, I also get, oops.

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So I can handle multiple errors the same way.

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I can also say as error here

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and just actually print out the error.

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And if I run this I'll get division by zero.

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Or if I do a string

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and run this I get the other error type.

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So this, again, is really useful to combine different errors

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if you wanna handle them the same way.

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But what if we actually wanna raise our own errors?

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That is we wanna throw our own errors.

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Maybe inside of this except block I

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actually want the error to display

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for certain types of errors.

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How could we do that?

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Let's find out in the next video.