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[no audio]

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Friends here we are going to

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discuss about exception handling with your

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Python. First of all, what is an exception? See simply, simply

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exception is nothing but an error and a Python program or

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script terminates as soon as it encounters an error. Assume

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that you have some ten or hundred or thousands of lines in

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your Python Script.

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[no audio]

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Maybe you have somewhere in your code error.

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If that error is encountered by your Python,

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then your script will stop. Your script won't execute.

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It will terminate, right.

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See let me show you with simple example.

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Let me save it as 'working_with_exceptions.py'.

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Now guys, first of all I am writing simply, see that

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[no audio]

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"Welcome to

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[no audio]

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exceptions concept".

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[no audio]

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Fine, let me run it.

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Yes, you are getting your output. Right. Assume that you

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have only one line in your code. No problem.

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Let me remove this parentheses at the end of your 'print'. Now

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see the result. You're getting an error. Because of that error

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you are going to stop your Python Script.

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Assume that you have one more line then. I will do one more

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thing. First of all

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I'm having.

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[no audio]

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Now it is fine.

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Let me save it and run it.

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Yes, you're getting two lines of output.

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But in the very first line what I am doing is, I am doing a mistake.

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[no audio]

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Now, you're not getting output for

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second line

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[no audio]

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See, while completion of your first line you did some mistake, right,

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because of that output, what is output you're getting?

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"SyntaxError". So you have some error somewhere. Because of that

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error your Python is going to stop your script. Right. Fine.

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Now, let me do it. Now, it's fine.

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Now, what I am doing is, 'print(, some 4/, or 4/2.

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Yes, you're getting result as 2.0. That's fine.

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Now instead of 2 I'm taking 0.

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Now see the result.

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[no audio]

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Again, you're also getting an error. That error is 'ZeroDivisionError: '.

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'division by zero'.

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See guys, if you compare in this way, let me remove here.

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What is output you're getting? 'SyntaxError'.

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Now if I do this thing, I mean divisible with 0,

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now you are getting 'ZeroDivisionError'.

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See previously you are getting 'SyntaxError', but now you are getting

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'ZeroDivisionError'.

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So basically errors are two types.

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In your Python,

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errors are two types.

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What they are?

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First one is

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'SyntaxError' or 'SyntaxErrors'

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Second one is, see guys,

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if you observe 4/2, it's working perfectly.

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That means perfect syntax

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is there. If I do with 0 as per syntax, it's correct, right?

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Maybe as per your mathematic rule it is not possible,

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but as per syntax it is correct.

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Now, while running you are getting an error because of 4

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division with 0 is not possible.

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That means while running you're getting a different type

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of error called 'ZeroDivisionError'.

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Now this type of errors are called runtime errors.

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See as per syntax it is correct, but while running because you

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don't have any defined value for 4/0, right,

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that's why you are getting an error.

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That's why this is a runtime error.

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[no audio]

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And these errors are nothing but exceptions.

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[no audio]

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This is an exceptional case, right. As per mathematic rule

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if 4/2 is possible,

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sorry 4/2 is possible but only 4/0

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is not possible, some exception.

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So exceptions are occurring only during runtime, right. Fine.

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See this syntax errors,

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you don't have any special rule to handle this syntax errors.

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That means you need to follow the syntaxes exactly while

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writing your Python Script. No way

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to handle syntax errors, but you can handle exceptions. You

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can handle exceptions. That means, see as of now you're getting

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suppose 4/0, some 'ZeroDivisionError'. That type

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of errors you can handle and instead of terminating your

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Python Script in this way

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you can terminate with meaningful information.

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[no audio]

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Right. So I will show you that. Before that there is a way

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to handle,

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[no audio]

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it's important guys, to handle runtime errors or exceptions.

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Let me show you with simple example.

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See what I am doing is,

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[no audio]

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don't worry about syntax.

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Just observe the output.

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I am printing simply 4/2.

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[no audio]

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Now I am simply printing.

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[no audio]

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Now previously you are getting your output in this way, some random

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message you are getting. Now you are not going to get. You

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are going to get. See that result first.

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It's perfect. Suppose if I do 4/0, what is happening?

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It is not giving an error.

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Of course, this is the error but we are handling that. We are giving

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with clear information 'ZeroDivisionErrors', or

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'ZeroDivisionError'. Now it is not like an error. Of course

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it is an error, but we are handling it carefully. Right. Fine.

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So first of all

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[no audio]

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How, when, when you have to use exception handling

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in your Python Script?

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Nothing is there guys. Very simple. Assume that you have a

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code. Assume that you have a code, and if there is a chance

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to get any runtime error, then you have to handle it.

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Very simple thing. One more thing.

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Let me do one thing.

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I want to open a file.

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I want to open a file called

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let's say 'open nari.txt', for read purpose.

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That's my default mode

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I am not mentioning. Then I am closing. Between these two

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let me print 'fo.read'.

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See the output. What you are getting.

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'FileNotFoundError'.

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Actually 'nari.txt' file is existing,

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then you don't have any error. As per syntax it is correct,

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but while running because there is no file you are getting an error.

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That's why this is a runtime error.

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So here there is a chance.

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What is that chance?

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Maybe 'nari.txt' file exists or may not exist.

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Right. So that's why you can expect here,

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yes, there is a chance to get an exception.

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That's why you can handle in this way.

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What is that?

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'try:'. 'try:', open your file,

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[no audio]

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then let me print content,

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[no audio]

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then let me close our file. If really file is there this code

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will execute otherwise

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'except:' let me write some, I don't know

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what is the error.

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Let me write, "Some problem while reading the nari.txt

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file". That's it.

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Now, let me run it.

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[no audio]

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Yeah, now it is 'SyntaxError'.

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What is that syntax error?

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[no audio]

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Print. Yeah, it's not 'for', right. It is simply 'fo'. Yeah.

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You can't handle syntax errors.

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So be careful while writing your syntaxes.

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You can handle only your runtime errors.

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That's what here I'm showing. See actually 'nari.txt'

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file is not there.

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If it is there what will happen? This block will execute. Then

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it will simply skip this line, simply 'except' block, it will

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simply skip 'except' block.

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If something goes wrong here while running your codes, then

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your Python will stop this part and then it will try to execute

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the code which is there in your 'except' block.

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So it's like a simple thing like if and else but you know

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in if and else what will happen? If 'if' condition is false, then

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only 'else' will execute but here not like that.

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Your Python will try to execute this block first. In this

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maybe at any line

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if something goes wrong, then your Python will stop the execution

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of this block and immediately

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it will try to execute the block which is there under your

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'except'. That's it.

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[no audio]

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Right. See now, what I am doing is I don't know

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what is the error I'm getting as of now.

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That's why you can also get what type of error you are going

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to get here 'except Exception',

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what is the exception?

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[no audio]

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as some error 'e', and you can print that

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[no audio]

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because of this error you are stopping, your Python is going

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to stop your code. See that, 'No such file or directory

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called 'nari.txt'.

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That's it. Actually this is a 'FileNotFoundError'.

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[no audio]

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If you don't handle with the 'try' and 'except' then see instead of

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[no audio]

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in a smooth way you are handling your code,

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if you use 'try' and 'except'. If you don't use that what will happen?

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[no audio]

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See that. Simply I'm doing this, no.

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[no audio]

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You're getting like 'FileNotFoundError:

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No such file or directory'.

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Of course, the error is fine,

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but you are not handling properly to run your code.

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That's the reason whenever there is a chance to get an exception

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while running your code, at that time

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please try to use 'try' and 'except' block.

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And, these are simple thing guys, 'try' and 'except' block.

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So let me write how to handle

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[no audio]

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exceptions. Simple, it is an interview question, guys. With the 'try'

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and 'except' block. That's it.

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[no audio]

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Right. Then, what is the syntax for that?

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Very simple.

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'try:', whatever the code you have just try to write in a 'try:'

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block. Let me write some line number 1 or statement 1. You

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can write any number of statements under this 'try:'.

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'statement-3', something like that.

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If something goes wrong with any one of the statement which

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are there under your 'try' block then your Python will

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automatically skip the 'try' block and then it will try to execute

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'except:' block. In 'except:' block you can write something.

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So, "This is

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[no audio]

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because of something

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went wrong

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[no audio]

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in try block".

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So what is that? This is just to tell that something goes

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wrong in your 'try' block.

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But what I want is I want to see exactly what is the error

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is there, then what is the syntax we have to use

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is, same syntax. Actually now, this is useful guys.

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This is useful in your real time.

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[no audio]

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But this is simple way. We will see advanced level as well.

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'except Exception as e'. So why I am taking 'e', you can take

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anything, but this is an error

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that's why just to represent that I am taking 'e' variable.

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Right. Now, instead of this message

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what I can write is

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See, "This is because of", "This is",

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Now you know what is the error?

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I mean your Python knows that. Your Python handles that with

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variable called 'e' with the help of 'Exception' clause here.

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"This is because of", right, so you can write simply this way. That's it.

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[no audio]

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Right. Okay.

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[no audio]

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Now, let me show you one more thing.

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I am going to comment entire code.

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[no audio]

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See, what I am doing is

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I have a list called

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'my_list='

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some values [3, 4, 5], and guys if I try to print 'my_list

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[1], or maybe 2, whatever it may be, you're going to get

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your output, right?

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'my_list[1]' is nothing but 4.

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But if I try to print 'my_list[4]', what is the result you are getting?

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As per syntax it is correct,

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but 'my_list[4]' is nothing but 5th value from your list.

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So we don't have five values in our list.

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How come this fourth value, fourth index value we can get?

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It's not possible, right?

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That's why what are you showing? 'IndexError: list index out of range'.

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[no audio]

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Right. See, what I will do is,

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I will try to print 'my_list' index of 4, in case if, I don't

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know how many values are there in 'my_list', just assume that. Somewhere

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'my_list' is there. I don't know. While writing our course you

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will come to know how many values. Sometimes you need to create

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dynamically your list based on some values.

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You don't know how many values are there.

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Logically, you need to get suppose some 5th value then

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what I will do is, I will try to print 5th value in this way,

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but there is a chance that is, you don't have any values inside

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of your list. Maybe you have only two values but you are trying

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to access 5th value.

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That's why what I am doing is

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'except Exception as e', then

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I am trying to print that 'e'. So that instead of getting an

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error, I can see some message. Of course,

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if you get an error you can, you're also going to see message,

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but the problem is you're going to terminate your script.

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But with exception handling, you're not terminating your script.

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See that, after 'try' and 'except', I am writing

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"This code will also execute".

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[no audio]

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Now see the result. You are getting an error like 'list index out of range'.

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This code will also execute. But instead of that, suppose

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if I don't have 'try' and 'except' block, and if I try to print

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directly from our list a value called 5th value see that what

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will happen. 'print(my_list[4])' I'm trying to print. See

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[no audio]

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index, 'list index out of range', and your Python

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program is terminating here itself.

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It is not trying to execute this one.

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[no audio]

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See actually do we have any dependency

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between this line and this line?

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No. Because here you are using list, but nowhere we are

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using list in 39th line.

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If you are not using then no problem,

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you can execute this line, no.

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Why should we stop your code?

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That's why, that's the reason we are using 'try' and 'except'

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block in your code.

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[no audio]

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Right. Fine. So simply.

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Yeah, see here.

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[no audio]

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This is the syntax, right.

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So 'try:', whatever the main code you have to run that code

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you just try to write under 'try:' block.

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[no audio]

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So in case if something goes wrong while running your code,

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then what you want to display, then that you have to write

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under 'except:' block.

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Right. So this is just simple thing to handle your 'try' and 'except',

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I mean to handle your exceptions, but you need to use 'try'

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and 'except' as 'except Exception as e' then try to print that

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error. This is useful.

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[no audio]

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Right.

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This one is important one.

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That's fine.

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Now, let me show you some of the examples where you are going

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to get exceptions. 'IndexError',

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we have seen that. 'ZeroDivisionError',

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we have seen that. 'ImportError', 'ValueError'.

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What is 'ImportError' means, just assume that you're trying

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to import some module,

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so if that module is already there with your Python as a

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default module, then you won't get any exceptions but assume

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that you want to read Excel sheets, to read Excel sheets suppose

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you need to use 'xlrd' module.

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This is not the default module with your Python, then

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while importing this module you will get an error, right?

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So whenever you are trying to import third-party modules,

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you need to use 'try' and 'except' block.

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Let me show you that as well.

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It's important one.

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So what I am doing is, let me comment once again your code.

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[no audio]

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Just assume that I need to import a module called, suppose

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some 'fabric'.

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[no audio]

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Let me run it.

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There is no module, right?

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No module named 'fabric'. 'ModuleNotFoundError'.

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[no audio]

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Right. See that. What I can do is in that case 'try:'

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'except Exception as e', then I am printing simply error.

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So instead of terminating by your Python

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we are terminating, we are stopping or skipping gracefully,

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right. So that is the way to use your 'try' and 'except' block. That's it.

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So I am giving just some of the errors - 'TypeError', 'NameError',

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'FileNotFoundError', something like that. Okay.

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So while going forward we will see different types of errors

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and how to handle them. And we have one more video on this just

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to handle directly the known errors, right? Okay, guys.

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Yeah, one more thing, 'IOError'.

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We will see them, all of them while going forward.

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Okay, don't miss next video, okay.

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Okay guys, thank you for watching this video.

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[no audio]