#44 Python Tutorial for Beginners | Decorators

[00:01] [Music]

[00:07] welcome back aliens my name is Devin

[00:09] Wendy and in this video we'll talk about

[00:11] one of the amazing feature of Python

[00:13] which is decorators nothing about this

[00:16] when you talk about functions functions

[00:18] are built to perform certain tasks right

[00:21] so example let's say we have this file

[00:23] and in this file we have a function

[00:25] which is predefined so let's get a

[00:27] function here and this will be for

[00:29] division of course you can write any

[00:30] complex code but just to keep it simple

[00:32] let's go for division and of course a

[00:34] division function takes two parameters

[00:36] so we'll take a and B and this will

[00:39] return the division of this two so we'll

[00:41] say return a divided by B simple code

[00:44] right of course you can make it complex

[00:46] you can go for complex code by just to

[00:47] keep it simple the got two lines a

[00:49] division which divides two numbers and

[00:51] then if you call this function if you

[00:53] say let's see if I pass for my two and

[00:56] if you run this code of course you have

[00:58] to also print and short frittering here

[00:59] let's print so if you call this function

[01:02] now let's right-click and say run you

[01:05] can see we got two points so this is

[01:06] what we wanted right we wanted the

[01:08] output okay that's great but what if if

[01:11] I pass the value which is two and four

[01:15] so what are you expecting the output

[01:17] here so the output which I'm expecting

[01:19] here is of course 0.5 because that's

[01:21] what you will get and you can see we

[01:23] call 0.5 so what if I say I want a

[01:26] different logic here the logic which I

[01:28] want is doesn't matter in which sequence

[01:31] I pass the value it should be always the

[01:34] numerator should be bigger than the

[01:35] denominator so example in this case if

[01:37] I'm passing 2 and 4 it should be reverse

[01:39] while dividing only when my numerator is

[01:42] less than denominator I want to swap

[01:44] them ok so in this case even if you are

[01:47] passing 2 and footage the dividend

[01:48] should be 4 divided by 2 okay so we can

[01:51] do that right we can have our own logic

[01:53] so just for the example we are going for

[01:55] this ok so what do you think what you do

[01:57] so of course as a user I should be

[02:00] passing 4 and 2 but let's say as a user

[02:02] I want to pass 2 and 4 it is your job

[02:04] developer to make sure that they are

[02:07] getting swept okay you will say ok it's

[02:09] my job I will do it so you will go to

[02:11] the existing code with the division and

[02:13] you

[02:13] say okay so before dividing those two

[02:16] numbers I want to apply a logic the

[02:18] logic is if a is less than B I just want

[02:23] to swap them and we know how to swap two

[02:24] numbers right we can simply say a comma

[02:26] B is equal to B comma a simple logic and

[02:30] then once you have done that if you're

[02:31] on this code you can see we called 2.0

[02:33] it was so simple right but we got a

[02:36] twist the twist is as I mentioned

[02:38] imagine this code the division code

[02:41] which you have here is not with you this

[02:44] is in some other file and you're

[02:46] importing it maybe you don't have the

[02:48] access for this function and maybe you

[02:51] don't want to change the code of the

[02:53] existing function so I want you to swap

[02:56] those two values without touching the

[02:58] new function is it possible and that's

[03:01] where decorators comes into picture so

[03:03] what the decorators

[03:04] so using decorators you can add the

[03:06] extra features in the existing functions

[03:10] I know that sounds weird but we can do

[03:12] that so just to explain that whatever

[03:14] you do is either create a new function

[03:15] now this will be a decorator for teams I

[03:18] will say we're quite a smart because it

[03:20] can change the code right so it's a

[03:21] smart Dave now what this smart do will

[03:24] get now smart Dave will do as the

[03:28] function or the parameter so let's pass

[03:31] the function here so it will accept a

[03:33] function again while we talk about that

[03:35] later so this mod deal will accept a

[03:37] function and then so if you want to

[03:40] change the logic you have to write a

[03:41] code right I want to do that in another

[03:43] function so we can write a function

[03:45] inside a function that's the beauty of

[03:48] Python so let's create a function here

[03:50] so we'll say def we can have any

[03:52] function name let's go for dinner

[03:53] because they're in a function and then

[03:55] this inner function will take the same

[03:57] parameter which is taken by Dave two

[03:59] parameters let's take a comma B the name

[04:02] should not be same but you can have any

[04:04] name but the number of parameter should

[04:06] be same so you are passing - you have to

[04:07] accept - now in this inner you can write

[04:10] the logic which you are trying to write

[04:11] in dev so which was if a is greater than

[04:14] P in this case you will swap them so

[04:17] swapping is a comma B is equal to B

[04:19] comma a just to remove these spaces

[04:21] there let's do that and that's okay

[04:24] which have a space here so you can see

[04:25] we are creating a smart function here

[04:27] which has enough function who is doing

[04:30] our job so this is the code which I want

[04:32] inside my dev now once you have done

[04:35] that you simply have to return so you

[04:37] have to return the function which you

[04:39] are accepting here basically you know

[04:41] you are actually calling Dave here so in

[04:43] the return you will pass that two values

[04:45] a and B the new values so the original

[04:47] values were 2 & 4 after swapping you're

[04:50] passing food & 2 so you are calling a

[04:53] function by passing these two values now

[04:56] this function is your D function but

[04:58] you'll be thinking how they are matching

[05:00] just give me some time and then after

[05:03] this you just have to return the inner

[05:06] function because that's the function

[05:07] which is actually doing the job for you

[05:08] okay

[05:09] but will this work let's try let's run

[05:12] this code and you can see you're still

[05:14] getting 0.5 is because there is no

[05:16] connection between this mod Dave and

[05:19] this Dave let's create that connection

[05:21] so what we can do is before calling the

[05:23] duty function we can say Dave is equal

[05:26] to let's make it smart so we can assign

[05:28] the function to a function because

[05:30] everything in Python is no object right

[05:32] so against the DV is equal to smart Dave

[05:34] in which you will passing the new

[05:36] function now this new function is the

[05:39] original function you have and this is a

[05:41] new one in fact you know just to give

[05:43] you an idea I'll make this as do one and

[05:46] let me call that function do one by

[05:48] passing two and four so basically we are

[05:50] calling div but indirectly okay so we

[05:53] are calling de one which is calling

[05:55] which is using this mod do function by

[05:57] passing the values it will swap the

[05:59] values in build and then it will

[06:00] actually call the do function at the end

[06:03] which will print the values let's run

[06:07] this code and you can see regard the

[06:09] output which is wrong that's weird

[06:11] okay I guess there is something wrong

[06:13] with the if condition my bad

[06:14] so if errors okay so as a programmer you

[06:18] always make mistakes right so you can

[06:19] see it should be less than right that's

[06:20] what you want to smell so if you have

[06:22] this code now or we got to that's what

[06:24] we wanted right in fact the amazing

[06:26] thing is you don't have to go for a new

[06:28] name you can actually replace with the

[06:30] original itself which is Dave Dave so it

[06:32] looks like we are calling this new

[06:34] function but no just before calling them

[06:37] we are

[06:37] changing the definition for D right so

[06:39] this is the old Dave we are making a new

[06:41] deal now so you can see record 2.0 the

[06:45] amazing part about decorators is you can

[06:46] change the behavior of the existing

[06:49] function at the compile time itself so

[06:52] that's the decorators for you so just to

[06:54] recap what we are doing is we are

[06:55] creating a new function which takes

[06:57] function as a parameter and that's the

[06:59] beauty that this is not possible in all

[07:01] the languages so yes we can do that in

[07:03] Python because python is also a

[07:05] functional programming and then we can

[07:07] define a function inside a function

[07:09] which is actually replacing the code of

[07:11] div behind the scene and then we before

[07:15] pausing deep we are saying Dave is equal

[07:17] to smart Dave and we are passing Dave so

[07:19] basically we are changing the way they

[07:21] works so that's how you can use

[07:23] decorators in Python I hope you got

[07:25] something about decorators in this video

[07:27] so I hope you are enjoying this series

[07:29] let me in the comment section and do

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