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[no audio]

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Friends, here we are going to discuss about one of the operation from your

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Sys Module, that is called 'sys.argv', 'sys.arguments'

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Now what is this? See 'sys.argv' returns a list that consists

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of command line arguments which are passed to your Python

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script. Simply it is giving a list means it is a variable

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now. Actually it is one of the operation from your Sys Module.

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We know operation may be a function or maybe a variable.

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So 'sys.argv' is giving a list.

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Right? So which consists of some command line arguments, which are

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passed to your Python script.

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So to understand this, first of all you have to know what

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is a command line argument, right?

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Let me open some script.

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Let me open my editor.

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So I am going to write a script called

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[no audio]

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'command_line_arguments', 'command_line_arguments.py', so

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something. I'm writing

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nothing is there. Simply I am writing, "hello".

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[no audio]

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That's it.

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Now, I am going to run from command line.

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So if you want to work, if you want to know command line arguments,

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always you have to run your script from command line only. Fine.

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See just now we have written a script called, this one.

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Nothing is there simply, print('hello').

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Let me run this 'python command_line_arguments',

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your script name, '.py'

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Yes, you're getting some output. Right. Now while running your

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script, while running your script by your Python interpreter,

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I am also passing some values called, suppose, "hi how are

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you", some 1 3 67,

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whatever it may be. See if I pass in this way just observe that do you

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have any disturbance with your script?

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Is there any wrong output? No, it's working perfectly.

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See after your script name if I pass some values

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they are not disturbing your script.

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First of all in this way

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if you pass, yes, actually that is the correct. You can pass in that way.

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There is no wrong in that. If it is wrong, then you have to

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get some error, right?

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You are not getting any error.

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That means yes, you can run your script by passing some values

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in this way. Now after your script name whatever you're passing,

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right, so these all are called command line arguments for

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your script. While running your script you're passing some

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values. These are called command line arguments, right?

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So if you are passing some command line arguments here, if

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you're passing some command line arguments here how you can

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get them inside of your Python script?

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[no audio]

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Right. See nothing

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is there. What I am doing is simply, now let me remove 'pring('hello')'.

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You can write anything, right?

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I am writing 'print(sys.argv)', that is a variable but

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you are using 'sys', right?

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That's why what you have to do? You need to 'import sys'.

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[no audio]

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Right? Now see. First of all observe your script, what you have inside

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of your script. Nothing is there. I am using 'sys'.

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That's why I am importing that 'sys' first. Then I am printing

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simply 'sys.argv'.

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First I am running your script in this way, guys. Observe

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the output what you are getting? You are getting a list which

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consists of your script name only because after your script

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name, you're not passing anything. In case if you pass what

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will happen? Just I am passing, suppose 'python',

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some 'shell', some 'perl', something like that.

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So we'll see the output. Whatever you are passing here,

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all these values are coming in this variable called 'sys.argv' as a list.

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Not only that, you can pass some values also, see the output.

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Now 'sys.argv' is capturing inside of your script

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whatever the values, whatever the arguments you are passing

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while running your script, right?

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So these are the command line arguments you are passing while

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running your script and you can handle these values inside

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of your script with the help of 'sys.argv'.

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It's very, very helpful.

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[no audio]

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Right? And you need to remember one more thing, whatever the

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values you are passing from command lines even though if

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it is a number see that it is treating as a string.

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That's why you have a quotation here. You know in Python,

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right, if I write x equals to some list consists of 4, 5

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then here 4 and 5 are values. Observe the output. You are

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not having any quotations. But here you having a quotation

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for your numbers,

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that means whatever you are passing from command line all

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will treat as a string by your Python, right. Fine.

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Let me take one simple example to understand this example.

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Yeah, one more thing guys. See, this is going to give all your

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command line arguments, right?

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And if you observe your output, the very first value is always

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your script. How many values you are passing?

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How many command line arguments you are passing?

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Right. Whatever you are passing,

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the index 0 is always your script name. See that. Now I am passing

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only one command line argument. You are getting index 0

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as your script name, remaining all are your command line arguments,

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right? So if I want to display only script name what I have

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to do? 'sys.', if you remember, if you remember list operations,

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I want to get only the first index value.

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I mean the first value in your list, that is index is always

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0, right?

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Let me rerun and see the output. Because of, let me open your

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script once again here, because of 'prints(sys.argv[0])' you are

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getting this command line arguments as a script name.

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0 is always script name in your 'sys.argv',

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because 'sys.argv' is a list, in that first value is

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always your script name.

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That's what I am getting with index 0.

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That's fine.

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Now guys, I have a small requirement.

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My requirement is, my script has to read some string,

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my script has to read some string.

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Then after that, I need to convert, based on my requirement

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sometimes I will convert into lowercase,

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sometimes I will convert into uppercase.

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sometimes I will convert into title format.

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Right. Forget about first your command line arguments.

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So if you want to provide some string to your script what

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you have to do?

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Let me do this thing.

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[no audio]

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Let me take 'usr_str =', if you want to read a string

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always you have to take 'input' as a, let me save it.

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[no audio]

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'actions_on_strings.py', right? See here.

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I am reading a string from command line, 'usr_str = input',

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enter your string, I am asking.

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Then after that, 'usr_action', I am reading. What is that action

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means, 'input("Enter your action

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[no audio]

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on your string", so "Valid actions are", just I am giving the

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clue. "Valid actions are:" like "lower/upper/title" format.

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That's it.

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So these are the values I need to read from user. Now assume

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that user is going to enter some string and user is going

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to enter suppose lower or upper or title format, now based on

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user request.

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I need to print your string in lowercase or uppercase or

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in the title format.

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That's why here I need to take 'if' condition first of all,

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right. 'if usr_action == lower',

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[no audio]

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right, then I have to print your given string, that is 'usr_str' into

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lowercase. We have different options here,

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right. User may enter, right 'upper' also. So I am checking

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'if usr_action == upper',

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then I am going to print my 'usr_str' in terms of uppercase.

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[no audio]

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Right. 'elif 'usr_action', if 'usr_action =="title"' format,

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then I am printing 'usr_str.title'. In case by mistake

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if user enters other than lower/upper/title,

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then I'm writing 'else' block, and I am saying

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"Your option is invalid".

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New Text

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Right, so "Please select valid options from this list".

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So what are the valid options? "lower/upper/title"

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That's it. Fine.

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Right, let me go and run this script from command line.

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So first of all your script, this is your script.

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Let me run it and see the output first.

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I am running. I am providing string called, some randomly

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I am providing in this way, "Python scripting", something like

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that. Then I want to convert my string into lower or upper

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or title. Any option

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you can provide. I am giving, suppose title format, then see

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the output. You're getting in the title format. Then I'm rerunning

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and now I am going to provide 'lower'.

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I want to convert my string into lower case. Yes, fine.

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[no audio]

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But whatever the script you have now your script needs two

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inputs - one is string, one more is user action. One is string

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one more is user action. But while running script you are

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providing, right.

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See after running I am interacting with my script.

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Yes, you can interact but my intention is I don't want to

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provide in this way.

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[no audio]

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I have to run with one step.

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I have to run my script in one step, then how you can do it?

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See for that I have a idea.

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What I will do is, first command line arguments

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I will send as a, I will send a string, required string like

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"Python scripting". Then second argument, right,

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I will provide action, like lower. Then I will enter so that

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it has to work.

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[no audio]

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Right. Now if you pass in this way you have to use your Sys Module,

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and you can handle them - string as your first argument, right

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and action as second argument.

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Now, what I am doing is, instead of using 'input' now I am going

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to comment these two things. Now, I am going to import your

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Sys Module, then 'usr_str' I am taking, guys is if you

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remember 'sys.argv'

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is going to give your all command line arguments, right.

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In that zeroth argument is the script name. Then see if you

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are running in this way,

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if you are running in this way, let me do that thing first, otherwise.

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I will comment your entire code.

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Right. Now what I am doing is I'm going to print your

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'print(sys.argv)' first

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Right. Now, let me run this and see the output.

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If you run in this way, you're getting a list inside of your

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script with the help of 'sys.argv'. In that index 0 is script

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name, index 1 is your given string, and index 2 is user

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action. That's what you are getting by running in this way

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with the help of 'sys.argv'.

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Right. So guys whenever if you want to pass an argument,

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which consists of some spaces then you have to write your

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entire string inside of quotation.

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Right. Now see. Now because with the help of 'sys.argv' you're

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able to get your command line arguments inside of your script.

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That's why what I am doing is, 'usr_str' I can assign index 1, right.

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So 'sys.argv' index 1 I am assigning for user string, and user action

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'sys.argv' index 2. That's it.

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Right. Now, let me run your script and see the magic. Now,

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I'm not going to use 'input' command, and I'm not going to provide

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multiple lines input for your script, only single step, just

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running this way. See the output. You're getting your string

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in lower case. Maybe you are getting confusion because the entire

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thing is in lowercase. Let me do

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[no audio]

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in this way.

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[no audio]

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Right. See the output. You are getting string in lowercase or

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let me pass here upper.

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[no audio]

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Let me past title.

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[no audio]

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Yes, it's perfectly working.

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[no audio]

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Right. But here a small drawback

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is there. What does that mean? By mistake suppose if I'm not

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passing this, you're getting an error.

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"List index out of range", because you are passing only script

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name and string name.

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What about action? Action is always index 2 position you

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have taken inside of your script, but you are not passing three

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values. If you pass three values, then you can take index

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3. You're passing only two values, that is script name and

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then string name.

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This is zeroth index.

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This is first index. Then what about second index? You are

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not passing, but you are sending that. You are sending that

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index 2 value to this action.

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So without having second index value, how can you assign

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that value to other variables? That's not possible.

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That's why you're getting an error.

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Right? So whenever if you are using command-line arguments with

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the help of 'sys.argv' you have to take care.

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What is that care? How you can take care, right? Nothing

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is there. Very simple. Observe that. So guys for our script

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for our script as of now, whatever we are working using lower/

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upper/ title format,

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how many command line arguments we need? One is script name,

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second one is string, third one is action.

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So three values you are passing then only it is correct.

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If you pass two values, then it is not correct.

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Even if you pass more than three, no need of four values.

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That's why what I am doing is, before running, before assigning

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your command line arguments to your variable,

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first of all I am finding, 'print("The number of command line arguments")'.

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[no audio]

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If you remember, if you have a list, if you have

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a list you can find out number of values in that by using

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'length' function.

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So 'sys.argv' is a list, right and I'm finding number of values.

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Let me comment your entire code first.

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[no audio]

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Now run your script and see the output.

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Yes, you are getting three because you're passing script

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name, first command line argument, second command line argument.

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If I pass in this way, what is that?

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[no audio]

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Yeah, with only, suppose something

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[no audio]

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then you're getting two. Whenever if you get two, that is not

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correct. You're not running your script in the proper way

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because you need three values finally here, including

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your script name - script name, your string, and then your action.

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That's why what I am doing is whenever if this value is not

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equal to 3, right. 'if', see that. 'if length' of your

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'sys.rgv', if it is not equal to 3, if it equals 3, no problem.

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If it is not equal to 3 then I can't assign second argument

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value to your user action.

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[no audio]

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Not equal to 3 means

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assume that you are sending only two values, then it's not correct

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no. That's why whenever if your number of arguments are

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not equals to three, maybe two or more than three,

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I need only exactly three including your script name - script

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name, string name, and action.

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It should have three only. In case if it is not equal to 3

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then I want to stop my script. You know, you can stop your

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script using 'sys.exit'. Previously

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we discussed this right in previous video.

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[no audio]

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Now, see the magic.

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Now you don't get any error. Previously whenever if you don't

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have this logic,

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let me cut it and save it and run it

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once again. You are getting an error, right? "index range"

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"IndexError: list index out of range".

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But what I am doing is I am saving this now with the help of this simple

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'If' condition. Now, I am running. You're not getting any error.

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Simply your Python is stopping your script whenever if you are not

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passing proper command line arguments. But simply stopping

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is not a good practice. Whenever if you're not passing exactly

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three arguments then simply you are stopping, right. Before stopping

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just try to write some message. 'print

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"Usage of this script". "Usage:". "Usage: is, 'print' your

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'sys.argv', 'argv', script name, then after that what you have to do?

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Right? Let me do 'f' strings.

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[no audio]

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So usage I'm writing, so print your script name then, then

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here you have to pass,

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pass your string.

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Your required string

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I'm writing suppose, "your required string" here.

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Then here you have to write action. Action is like lower or

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[no audio]

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upper or title.

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That's it.

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Now, I am saving this and I am going to run. Guys try to understand

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this. It's very useful.

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I am running in this way.

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Then you are getting usage is, you have to run this script

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in this way, "action_on_strings.py", then your string, then some action.

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you have to provide like lower or upper or title.

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Now, I am going to provide in the proper way. Suppose

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I am running upper, now it's working properly.

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If you are not passing command-line arguments perfectly,

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then only are getting usage,

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otherwise it's working perfectly, right?

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So guys finally here

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we got the concept of 'sys.argv',

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and 'sys.exit' as well.

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So that's why 'sys.exit' is, 'sys.exit'

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is very helpful in your real-time. Why we are using? Just

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to stop your script. When we are stopping?

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If you are not passing proper command line arguments.

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If you are not passing proper command line arguments what

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will happen? Because of this line you are getting an error.

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I don't want to get an error.

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Right? That's why. When you will get an error? If you are not passing

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proper arguments.

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So whenever if you are not passing proper arguments, I am

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going to stop my script by simply saying this information to the user.

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"Please run this script in this way". Usage of script

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I am giving, and then I am stopping. Then next time whenever

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the user is going to run your script

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he will take care how to run a script, right? Okay.

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Okay guys, thank you for watching this video.

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It is very, very important while writing your scripts

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'sys.argv', right. Fine.

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[no audio]