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[no audio]

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Friends, here we are going to

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discuss about Python functions concept, simply

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introduction part with your functions. Before going to work

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with your functions,

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let us assume that we have some code which consists of

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suppose some 150 lines.

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So I have 150 lines of code.

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And if you observe this entire code, somewhere I am repeating

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same logic in different places.

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Assume that, same logic I am repeating in 3 places.

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Assume that each logic consists of suppose some 30 lines.

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That means, the same 30 lines of logic you are repeating in 3 places.

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Not only 3, just assume that some number of

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times you are repeating same type of logic.

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Right. See if you are repeating the same logic in different places,

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in that case you don't need to write your logic in 3 places whenever

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if you are repeating. What we will do is, whatever

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the logic you are repeating no, that logic I will write

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in one place in my code itself, and I will give some name

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suppose for that 'mycode'.

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[no audio]

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And now what I will do is, I will remove these 30 lines of

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code in 3 places.

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Wherever you have

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30 lines of code, right, there simply I will write 'mycode'.

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I have given a name for 30 lines of code, 'mycode'.

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Now here I am giving 'mycode'.

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[no audio]

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'mycode',

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Right. Now guys, what I am doing is, see, actually you have

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150 lines of code, in this 150 lines of code, 30 + 30 + 30, 90,

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90 lines, plus remaining 60 lines, finally 150 lines of code.

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But 30 lines of code we are repeating in 3 places.

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That means, instead of these 90 lines,

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what we are doing is 30 lines of code

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I'm writing somewhere.

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Wherever this 30 lines of code is required, there

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I will write the name which I have given for this 30 lines of code.

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So, what is the name I have given? 'mycode'.

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So here I will write 'mycode'. Instead of 30 lines simply I'm writing only

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one line. So, you are saving 29 lines.

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You're reducing 29 lines in this place. Same way in this 30

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lines, I am removing these 30 lines.

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Simply I'm writing 'mycode'.

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That's it. I'm giving the name.

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Then again here also, reducing 29 lines.

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So then here also you are having 30 lines no,

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I am removing these 30 lines of code and simply

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I'm writing whatever the name I have given for this 30 lines,

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'mycode'. Then here also you are reducing 29 line numbers.

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So instead of 90 lines, now you are using only 3 lines,

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plus in the same code itself you are giving a name for your

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30 lines. 30 lines plus name, 31 lines.

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So finally you're writing 34 lines instead of 90 lines.

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[no audio]

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So you almost reduced 60, 56 lines, right?

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So you are able to reduce your length of the code.

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Let me give a simple example.

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You can easily understand that. Suppose

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I have a small requirement. The purpose of requirement,

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I mean the requirement is, whenever I run my Python script,

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it has to clear my command line, then it has to display the

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list of files and directories.

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Right. See that I am writing

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[no audio]

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something like,

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I need to run commands like 'cls', suppose Windows,

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I need to run 'cls' command, and then 'dir' command. Right.

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So, to run your commands, you have two options in your Python.

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'os.system()', and then sub-process module.

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Of course, you are also having 'os.popen', process open,

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but anyway, 'os.system()', and sub-process are the best

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[no audio]

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process to run your commands. And whenever you want to

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capture the output, then go with the sub-process. Just simply

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if you want to run the command, just go with 'os.system()'.

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That's why here my intention is,

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just I want to run the command.

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So, I am importing 'os'. So simply 'os.system("cls")' I am running. Then

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'os.system()', what I am running, 'dir' command, that's it.

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Now, let me go to command line. And then, so I have given script

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name as 'run_ your_commands.py'. Now let me run it. Yes.

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It's clearing your screen and it is displaying something.

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But I want to display something like 'print("Please wait")'.

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Actually, no need of this, just for clarity

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I'm giving number of lines. "Please wait.

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[no audio]

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Cleaning the screen". That's it.

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Then after this, 'print(

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"Please wait. Finding the list of directories and files")'.

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[no audio]

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That's it. Now, let me run it.

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[no audio]

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Yes, you are getting. But after displaying, "Please wait

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finding the list of directories and files",

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I want to wait for 2 seconds before executing the next line,

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I mean before executing this line. The same way

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after printing this line

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I want to wait for 2 seconds before executing this

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'os.system()', so that I can see this information.

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Otherwise, this information is also going to clean on your command line.

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So, to wait for sometime you have a 'time' module.

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Anyway, we'll discuss about 'time' module in detail.

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[no audio]

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So, what I am doing is, after displaying this

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messages, I don't want to go and execute next line,

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I want to wait for 2 seconds.

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I want to stop your process with your Python. Then simply

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'time.sleep(2)' seconds I want to wait.

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The same way after displaying this message,

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I want to wait again suppose, sorry 'time.sleep(2)' seconds.

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

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So, it's waiting 2 seconds. Then after that, it is waiting

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again 2 seconds. Then you're getting your data.

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That's fine.

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Suppose if I copy this code, and if I try to run this on my

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Unix-like system,

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[no audio]

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Right. Let me write simply 'run_your_commands.py' script.

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So same script I am copying and pasting here.

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Will it work? See the result. So I want to run using Python 3.

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[no audio]

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See, 'cls' command is not working, because 'cls' is not the

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command to clear your command line of your Unix-like system.

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'clear' is the command, right?

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And anyway 'dir' is working. But I want to get in detail,

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in this way I want to get. Then you have to use 'ls - lrt'.

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So, on Windows you have 'cls' and 'dir'. For Unix

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I need 'clear' and 'ls -lrt' commands.

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So, what I am doing is, before running your commands

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I'm trying to identify the platform. You know there is a 'platform' module.

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And if you remember, we discussed already about this.

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Right. "Windows". So, if 'platform.system() == "Windows",

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then I want to run this logic.

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[no audio]

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See the logic.

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[no audio]

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That's it. 'else', if it is not Windows, what I am doing is, same logic

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but difference in commands. See that.

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Same logic, the only thing here 'clear', and here 'ls-lrt'.

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Now, first let me save it.

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So guys, how we designed our script?

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It's like a platform independent script. It will execute on

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your Windows, as well as Unix-like systems.

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And what is finally your purpose? Clear your screen, then

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list the directories and files in the current location. Yes.

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Now I am running our script.

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[no audio]

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"Clearing your screen...". Wait 2 seconds. "Finding list of directories

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and files." Then you are getting. Now,

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what I will do is, I am going to copy this script to your

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Unix-like system as well.

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So before that, let me clean your old data. Now I am going

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to open same script,

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I am going to copy and paste the code which you have

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on your Windows. Now same logic, same script I'm running now on

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your Windows, sorry, Unix-like system.

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Now it's working, see that.

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That's fine.

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But the problem is, if you observe your entire logic,

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if you observe your entire logic,

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see, if you clearly observe, this thing,

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[no audio]

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right, and this thing,

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[no audio]

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same logic you are repeating here and here. The only thing,

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commands are different. This command, this command is different.

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Windows, this command. Unix, this command. Windows 'dir' command,

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Linux 'ls -lrt' but remaining logic is same no.

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That means you are repeating same logic in two places.

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As of now, only in two places, maybe in real time you

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are going to repeat same kind of logic maybe 100 times,

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or 10 times, or 5 times, based on your requirement.

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[no audio]

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As of now, I am repeating my logic in two places. Forget about

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commands, logic is same no.

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So, what I will do is, in my code itself right, this logic,

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I will write somewhere with some name, with some name.

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I am giving name for that suppose 'mycode'.

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You can provide any name for that.

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Okay, we will learn in detail about how to

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define your name for your logic.

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Everything we'll learn while going forward. For time being just

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observe the logic.

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[no audio]

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That's it.

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Now instead of, now forget about this 'cls',

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I am taking that as 'cmd1', and I am taking this as

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'cmd2'. Okay.

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Don't worry why we are taking 'cmd1' and 'cmd2'.

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We'll discuss in detail while going forward. But here my intention

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is, if you are repeating the logic, why should we repeat that logic?

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I don't want to repeat.

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[no audio]

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Right. See, actually whatever the logic you are repeating, that I removed.

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Right. But this is the logic you are repeating, right,

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that's why what is the name you have given for this logic?

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This is the name you have given.

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That name I will write here and here. That's it.

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So that your logic is over, but how is it going to work?

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We'll discuss it. 'mycode', then here I'm also writing 'mycode'.

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Now internally Python will replace

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in place of 'mycode' this entire logic.

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Same code only, you are not disturbing anything.

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The only thing, you are reducing the number of lines.

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Instead of rewriting the same logic in different places, what we are

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doing? We are writing in one place, and we are giving some

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name for that. Whenever it is required in your code instead

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of writing that entire logic simple

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we're writing the name which you have given for your logic.

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Right. So for this, I have given a name called 'mycode'.

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That's what I am writing here and here.

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Now internally have to assume that 'mycode' is nothing but

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this entire lines you can assume in place of 'mycode', and

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here also in place of 'mycode', we can assume entirely these lines.

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So, finally you are not disturbing with your code. Right.

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Whenever I'm working with Windows, I need to run something

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like 'cls'. Don't worry how I am giving this syntax.

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Okay. Just observe the concept. That's it.

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We'll discuss in detail.

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[no audio]

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That's it. Let me save it. So guys what I am doing,

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observe that. The logic which you are repeating, that logic

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I have written somewhere, and I have given some name for that.

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So, in your code previously wherever you are using this logic

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in that place simply I am giving this name. That's it.

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Now let me run it. If it is working perfectly then

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the way which you used here, that's correct.

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Right. Yes, it's working. See that.

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That means, whatever the process we followed, that is correct.

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So if we follow this process, what is the advantage? You are

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going to reduce the number of lines, or in reverse way, you

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are able to reuse this logic any number of times in your code.

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That is the advantage. Wherever you need

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there you don't need to write it no, simply

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you are going to you use this name.

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Reusability. Right. Now,

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let me copy this code to your Unix-like systems as well.

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There also I want to run it.

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[no audio]

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Let me copy and paste it.

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Right. I'm going to run it.

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So here also it is going to work perfectly. See that.

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[no audio]

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That's it.

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Right. So guys, in case you use this concept, then this is called a function.

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And you can reuse this function any number of times in your

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code wherever it is required.

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[no audio]

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Right. So how to define, how to use them, all those things, we'll see.

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[no audio]

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Okay, and one more thing,

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this is a function. Simply,

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this is a function. You know function means some operation

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is there with function. That's it. Suppose if you take

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'f(x) = 3x + 2', 'f(x)' is a function, and its operation

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is '3x + 2'. Now here 'mycode' is a function. That is nothing

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but 'f(x)', if you compare with your mathematics. 'mycode'

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is a function that is 'f(x)'. Right. 'mycode' is simply 'f', here

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'cmd1', 'cmd2', assume that 'x'. Now based on

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'x' you are getting your 'f(x)' value

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by executing this '3x + 2' expression. The same way, based

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on 'cmd1' and 'cmd2', you're getting final result for

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your 'mycode', by executing this logic.

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Right. See, if you are good with your mathematics,

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it is very easy to compare. Just assume that '3x + 2' is nothing

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but this part, 'mycode' is nothing but 'f',

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and 'cmd1', 'cmd2' are nothing but 'x'.

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So '3x + 2' depends on 'x' value. So based on

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'x' value finally you are getting 'f(x)' value. The same way this

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logic depends on 'cmd1' and 'cmd2'. Based on this

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'cmd1' and 'cmd2', finally you are getting the result of 'mycode'.

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That's why this is simply a function. Same as your mathematics

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concepts. That is on paper. This is on memory. That's it.

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You're executing with your Python software. That's it.

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So this is a function. Right.

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This is some variables as of now, but not variables,

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we have some other name. We'll see that. In 'f(x)', 'f' is a function,

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'x' is the variable. Same way,

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this is a function in terms of 'cmd1' and 'cmd2'.

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That's it.

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Right. So finally, I want to give you the simple definition for

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your function. Function is a block of code for some specific

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operation. That operation may be anything

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based on your requirement in your situation.

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Right. Once if you define a function, you can reuse that. Any

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number of times you can use it in your code wherever it is required.

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Right. And a function executes only when it is called.

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See that.

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Let me remove this.

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Don't worry how to call, we'll discuss that. So as of now just

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I defined a function. Nowhere I am using this, right.

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Am I using it here?

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So, previously you where using here and here, 13th line, 15th line.

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Suppose if I comment this code, nowhere you are using that.

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If you are not using, then if you run your code, it won't

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execute. Even, let me run it on your command line,

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then you will get a clarity.

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[no audio]

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Right. It's not executing. Even though if you have a function,

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it won't execute by itself.

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If you want to execute a function, you should use that

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somewhere in your code. That's it.

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That is the concept of your function. Okay.

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So guys, this is simply introduction part with your functions, okay.

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In later videos we will go with step-by-step,

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and we will learn completely about your functions. Right.

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And then we will see how to use in real-time

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for different scenarios, okay.

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Okay guys, thank you for watching this video.

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[no audio]