Exception Handling in Python |Section 2|Celestial Warrior

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Hi again! Let's have one more lecture

about errors in Python and this

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particular lecture will be about

handling errors. Handling errors can be

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an advanced concept to digest for now

because you're still going through the

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basics of Python and you haven't seen

any real application yet, but later

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will use error handling while we are

building real-world applications so

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you're going to understand error

handling better later on. For now let's

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just focus on the syntax and try to

understand as much as you can

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I'll go and do an example here which I

mentioned earlier. Let's say we have a

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function that does division between two

given numbers like that. Return a divided

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by b and then you call the function here.

Divide 1, 2. In this case the

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function will try to divide 1 by 2.

And let me print out the output so that

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we can see it on the terminal. Go to the

terminal and execute the script. So you

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get you get 0.5. Now that's good.

However if the user enters let's say

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zero there like that, execute and your

program will crash so it will show an

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error. Now this one here is an example of

a longer error message that I mentioned

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previously in the previous videos that

you might have more than one, more

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than one error in your traceback, so for

instance this says line 4 at this line

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here. So that line is where Python

captured the error at first

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so basically Python was trying to

execute this line but it couldn't do it,

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it didn't manage to do it because this

line was trying to get the information

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from this function

and this function was trying to do this

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mathematical operation using zero after

the division so that is not possible and

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Python is pointing that out here.

So that's the main error in line two

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in this expression so that's where you

should focus, however when you ask

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questions you should include the entire

error message in your question

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as I mentioned previously.

So back to handling errors now. What I'm

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trying to say here is that you know

you have other functions here and other

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lines of code that you want to execute,

that you want Python to execute, but if

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the user passed this zero number here

the other lines would not be executed

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so your program would crash and you

don't want that and the way to avoid

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that is by using try and accept so

basically you try to capture the

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exception, to handle the exception.

The way to do that is quite easy.

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You say try and return a/b, so this has to be

indented like that so try is indented

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because it's under the function

definition. And then return is indented

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because it's under the try expression.

Then you have except, execute so this

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has to be on the same indentation level

with try, they are the same block, so

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except if there is an exception. What you

want to do is print out: "You are

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dividing by zero", or

"is this meaningless". So let me try

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this now and you get: "Zero division is

meaningless" and none, oh sorry I meant

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to do here return, not print.

I explained you why you get none there so you

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got none as an output because what

the function did was its tried to do

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this expression but it got an error

so it ignores this line, it doesn't

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execute it and then it goes to the

next line. So this line is executed when

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this is not executed and so it printed

out: "Zero division is meaningless", but it

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also printed out none because when you

execute a function that doesn't have a

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return statement such as in this case we

had the print statement here, the print

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function not the return statement, in that

case if the function is not returning

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anything it can have a print function or

other function as well, but if it

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doesn't have a return statement

then it will print out none, so basically

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it executes the other procedures such as

the print statement, it prints out the

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statement but if it doesn't have

a return statement it doesn't, it prints

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out none. Anyway save this now, execute

again and in this case you get only this

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zero division is meaningless printed

out there. So basically if you had other

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lines of code here like that, those would

be executed as well and that happens by

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using the try and except block who which

make sure that the code flow continues.

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So while the important thing to note is

that it is advisable to actually here use

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the exact name of the error that you

want to accept, so

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Zero Division Error and as you see these

got turned into blue which means that

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this is actually a Python keyword, is

recognized by Python and in that case if

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you exact you this you get the same

output actually like that or if you pass

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a number there that it is possible to

get a division from, you'll get that.

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Sorry about the backslash. I typed that

by mistake on my terminal. Execute

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again so you get this. And so what I'm

trying to say about the zero division

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error is that you know sometimes you

might get other types of errors in your

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code, other types of exceptions.

Let's say you have a name error there

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and you are saying that except all

errors when you don't pass this you

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you're basically including all types of

errors there and that is a bit dangerous for your

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code because you know you might have

problems that you don't notice and

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basically you are ignoring that, but you

shouldn't. So you should be specific

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there, explicit like that. If there are

other types of errors such as a name error,

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that name error will crash your

program, so you know what's going on.

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You need to be specific.

If you want to handle that error too, then

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you can add another exception here.

Except name error for instance. Yeah,

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that's about handling errors in Python.

I hope this makes sense! I hope I explained

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this well! And yeah, this is about errors.

I'll talk to you in the next lectures.

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See you!

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