[0:01] [Music]
[0:07] welcome back aliens my name is Devin
[0:09] Wendy and in this video we'll talk about
[0:11] one of the amazing feature of Python
[0:13] which is decorators nothing about this
[0:16] when you talk about functions functions
[0:18] are built to perform certain tasks right
[0:21] so example let's say we have this file
[0:23] and in this file we have a function
[0:25] which is predefined so let's get a
[0:27] function here and this will be for
[0:29] division of course you can write any
[0:30] complex code but just to keep it simple
[0:32] let's go for division and of course a
[0:34] division function takes two parameters
[0:36] so we'll take a and B and this will
[0:39] return the division of this two so we'll
[0:41] say return a divided by B simple code
[0:44] right of course you can make it complex
[0:46] you can go for complex code by just to
[0:47] keep it simple the got two lines a
[0:49] division which divides two numbers and
[0:51] then if you call this function if you
[0:53] say let's see if I pass for my two and
[0:56] if you run this code of course you have
[0:58] to also print and short frittering here
[0:59] let's print so if you call this function
[1:02] now let's right-click and say run you
[1:05] can see we got two points so this is
[1:06] what we wanted right we wanted the
[1:08] output okay that's great but what if if
[1:11] I pass the value which is two and four
[1:15] so what are you expecting the output
[1:17] here so the output which I'm expecting
[1:19] here is of course 0.5 because that's
[1:21] what you will get and you can see we
[1:23] call 0.5 so what if I say I want a
[1:26] different logic here the logic which I
[1:28] want is doesn't matter in which sequence
[1:31] I pass the value it should be always the
[1:34] numerator should be bigger than the
[1:35] denominator so example in this case if
[1:37] I'm passing 2 and 4 it should be reverse
[1:39] while dividing only when my numerator is
[1:42] less than denominator I want to swap
[1:44] them ok so in this case even if you are
[1:47] passing 2 and footage the dividend
[1:48] should be 4 divided by 2 okay so we can
[1:51] do that right we can have our own logic
[1:53] so just for the example we are going for
[1:55] this ok so what do you think what you do
[1:57] so of course as a user I should be
[2:00] passing 4 and 2 but let's say as a user
[2:02] I want to pass 2 and 4 it is your job
[2:04] developer to make sure that they are
[2:07] getting swept okay you will say ok it's
[2:09] my job I will do it so you will go to
[2:11] the existing code with the division and
[2:13] you
[2:13] say okay so before dividing those two
[2:16] numbers I want to apply a logic the
[2:18] logic is if a is less than B I just want
[2:23] to swap them and we know how to swap two
[2:24] numbers right we can simply say a comma
[2:26] B is equal to B comma a simple logic and
[2:30] then once you have done that if you're
[2:31] on this code you can see we called 2.0
[2:33] it was so simple right but we got a
[2:36] twist the twist is as I mentioned
[2:38] imagine this code the division code
[2:41] which you have here is not with you this
[2:44] is in some other file and you're
[2:46] importing it maybe you don't have the
[2:48] access for this function and maybe you
[2:51] don't want to change the code of the
[2:53] existing function so I want you to swap
[2:56] those two values without touching the
[2:58] new function is it possible and that's
[3:01] where decorators comes into picture so
[3:03] what the decorators
[3:04] so using decorators you can add the
[3:06] extra features in the existing functions
[3:10] I know that sounds weird but we can do
[3:12] that so just to explain that whatever
[3:14] you do is either create a new function
[3:15] now this will be a decorator for teams I
[3:18] will say we're quite a smart because it
[3:20] can change the code right so it's a
[3:21] smart Dave now what this smart do will
[3:24] get now smart Dave will do as the
[3:28] function or the parameter so let's pass
[3:31] the function here so it will accept a
[3:33] function again while we talk about that
[3:35] later so this mod deal will accept a
[3:37] function and then so if you want to
[3:40] change the logic you have to write a
[3:41] code right I want to do that in another
[3:43] function so we can write a function
[3:45] inside a function that's the beauty of
[3:48] Python so let's create a function here
[3:50] so we'll say def we can have any
[3:52] function name let's go for dinner
[3:53] because they're in a function and then
[3:55] this inner function will take the same
[3:57] parameter which is taken by Dave two
[3:59] parameters let's take a comma B the name
[4:02] should not be same but you can have any
[4:04] name but the number of parameter should
[4:06] be same so you are passing - you have to
[4:07] accept - now in this inner you can write
[4:10] the logic which you are trying to write
[4:11] in dev so which was if a is greater than
[4:14] P in this case you will swap them so
[4:17] swapping is a comma B is equal to B
[4:19] comma a just to remove these spaces
[4:21] there let's do that and that's okay
[4:24] which have a space here so you can see
[4:25] we are creating a smart function here
[4:27] which has enough function who is doing
[4:30] our job so this is the code which I want
[4:32] inside my dev now once you have done
[4:35] that you simply have to return so you
[4:37] have to return the function which you
[4:39] are accepting here basically you know
[4:41] you are actually calling Dave here so in
[4:43] the return you will pass that two values
[4:45] a and B the new values so the original
[4:47] values were 2 & 4 after swapping you're
[4:50] passing food & 2 so you are calling a
[4:53] function by passing these two values now
[4:56] this function is your D function but
[4:58] you'll be thinking how they are matching
[5:00] just give me some time and then after
[5:03] this you just have to return the inner
[5:06] function because that's the function
[5:07] which is actually doing the job for you
[5:08] okay
[5:09] but will this work let's try let's run
[5:12] this code and you can see you're still
[5:14] getting 0.5 is because there is no
[5:16] connection between this mod Dave and
[5:19] this Dave let's create that connection
[5:21] so what we can do is before calling the
[5:23] duty function we can say Dave is equal
[5:26] to let's make it smart so we can assign
[5:28] the function to a function because
[5:30] everything in Python is no object right
[5:32] so against the DV is equal to smart Dave
[5:34] in which you will passing the new
[5:36] function now this new function is the
[5:39] original function you have and this is a
[5:41] new one in fact you know just to give
[5:43] you an idea I'll make this as do one and
[5:46] let me call that function do one by
[5:48] passing two and four so basically we are
[5:50] calling div but indirectly okay so we
[5:53] are calling de one which is calling
[5:55] which is using this mod do function by
[5:57] passing the values it will swap the
[5:59] values in build and then it will
[6:00] actually call the do function at the end
[6:03] which will print the values let's run
[6:07] this code and you can see regard the
[6:09] output which is wrong that's weird
[6:11] okay I guess there is something wrong
[6:13] with the if condition my bad
[6:14] so if errors okay so as a programmer you
[6:18] always make mistakes right so you can
[6:19] see it should be less than right that's
[6:20] what you want to smell so if you have
[6:22] this code now or we got to that's what
[6:24] we wanted right in fact the amazing
[6:26] thing is you don't have to go for a new
[6:28] name you can actually replace with the
[6:30] original itself which is Dave Dave so it
[6:32] looks like we are calling this new
[6:34] function but no just before calling them
[6:37] we are
[6:37] changing the definition for D right so
[6:39] this is the old Dave we are making a new
[6:41] deal now so you can see record 2.0 the
[6:45] amazing part about decorators is you can
[6:46] change the behavior of the existing
[6:49] function at the compile time itself so
[6:52] that's the decorators for you so just to
[6:54] recap what we are doing is we are
[6:55] creating a new function which takes
[6:57] function as a parameter and that's the
[6:59] beauty that this is not possible in all
[7:01] the languages so yes we can do that in
[7:03] Python because python is also a
[7:05] functional programming and then we can
[7:07] define a function inside a function
[7:09] which is actually replacing the code of
[7:11] div behind the scene and then we before
[7:15] pausing deep we are saying Dave is equal
[7:17] to smart Dave and we are passing Dave so
[7:19] basically we are changing the way they
[7:21] works so that's how you can use
[7:23] decorators in Python I hope you got
[7:25] something about decorators in this video
[7:27] so I hope you are enjoying this series
[7:29] let me in the comment section and do
[7:31] subscribe for further videos