Python Decorator Tutorial | Decorators in Python For Beginners | Python Tutorial | Edureka Rewind

Key Takeaways

hello everyone this is Wasim from Eda and I welcome you all to this session where I'll be talking about python decorator so without wasting any more time let's take a look at the agenda for this session so first of all I will start with the prerequisites that are python functions and then I will talk about python decorators with a few examples and finally I will discuss a rather complex concept that is fancy decorators with a few examples as well I hope you guys are clear with the agenda so without wasting any more time let's start our session I'm sure most of you are familiar with functions in Python so let's recall some of the important Concepts that are going to be useful while working with the decorators so the concepts that I want to discuss are first class objects and inner functions so in Python literally everything is treated as an object including all the data types and even functions so the functions can be passed around as arguments as well so that is why it is called a first class object coming on to the inner functions a function can be also declared in another function which is is known as an inner function it also resonates Around The Decorator so we'll get to that later on in the session so let's take it up to py charm and understand how inner functions work and we will also try to return a function from a function which is actually passing a function as an argument so let's take it up to py charm guys so now that we are in the py charm let me go to the presentation mode so that the clarity will be better so first of all let me talk about the first class object so I'll just take a function name it as let's say function one and inside this I'm going to pass a variable name so now I just want to return let's say hello so for this I'm going to use the string interpolation if you're not sure about that please do check out the tutorial on strings on Eda so that you'll be familiar with what I'm doing here that is the string interpolation you'll see what it does now let me Define one more function let's say Define function number two and inside this I'm going to pass the same argument that is name and now I'm going to return using the string interpolation again so after this I actually want to ask how you doing I have to give two lines over here this should do and now I want to take one more function guys so I'll name it as function number three and inside this I'm going to pass function as an argument so here I just want to return function number four and inside this let's say I want to write DL Ono now when I print this I'm going to print function number three and inside this I'm going to pass function that is function number one now again I'm going to pass function number let's say three and inside this I'm going to pass the function number two again let's see what the output is okay we have an error guys function two is missing one required positional argument name so we have made a mistake over here so when I print this now I'm getting the output as hello dear learner and dear learner how you doing so I'm actually able to pass the functions as arguments so that is actually how we use the first class object we can use anything as an object in Python now moving on to the next example that I'm going to show you is for inner functions so how exactly do you use inner functions so I'm going to take one function let's say fun and inside this I'm going to Define one more function so first of all Let me give it a statement I'll say first function and after this I'm going to Define one more function and this is going to be function number two or I'll just write it as function number one and after this I'm going to give one more statement over here let's say first child function now I'm going to Define one more function let's say function number two and inside this I am going to print let's say second child function and let me take one more statement so function two and function one now when I print our function over here let's see what the output is so first of all we are getting first function that is the base function and then we are getting the child function and the first child function so this is how you can use inner functions in Python basically it's a nested functions we are using multiple functions inside a function so we have one function over here and inside this we have two more child functions so this is a basic example of inner functions and python decorators is going to revolve around this concept A Lot the first class objects and in the functions that is why I was telling you about this I'm going to show you one more example so I'm going to return a function from a function so basically what it means means is I am taking a function as an argument for another function so what I'll do is I'll just write function and Define one function over here I'll just write n and now I'm going to Define one more function let's say function number one so I'm going to return let's say urea yes and now I'm going to take one more function let's say function number two and inside this function I'm going to return let's say Python and now let me take a statement guys so if n is equal to let's say one so I'm going to return function number one I'll not use this I'll tell you about this later else I am going to return function two so this is my function guys inside this I have two more functions I'll show you what it does so I have a is equal to function and inside this I'll write one and now again inside this I'll write let's say two so now when I print a and let's say I'm want to print b as well you'll see what the output is okay we have uh name B is not defined so actually I had to take B over here so the output is Eda and python so I'm successfully able to return a function from a function guys so I've taken these two functions as arguments and this is how we can return a function from a function so now that we are through with the python prerequisites we'll talk about decorators in Python a decorator is a design pattern in Python that allows a user to add new functionality to an existing object without modifying its structure so decorators are usually called before the definition of a function you want to decorate let's take a simple example to understand how it works so we'll go to pyam again I'll clear this off and okay let me just put it right here now I'm going to take a simple decorated example so I'll just Define a function yes and and inside this let's say I want to pass a function as an argument I'll name it as function one now again I'm going to define a wrapper function this is my inner function guys and this is basically The Decorator that I'm going to use here I'm going to pass function again so you'll see what it does and I'm going to print one more statement off this so let's just say welcome to Python edura tutorial now I'm going to return rapper over here and I'm going to Define one more function and inside this function number two I'm going to use a print statement let's say pythonista and let's just call a function Now function number let's say two is equal to function 1 function two so this is a very important state guys now I'm just going to call the function number two let's see what the output is so my output is hello pythonista welcome to python Eda tutorial so as you can see inside the rapper function over here first of all we are getting hello after that the function which we have right here this one function number two which we have passed in function number one so this is my RPP statement guys there is another approach to this using a pi syntax or we can call it a syntactic sugar as well so it basically makes it easier to use decorators in Python guys what I'm going to do is I'm going to make a few changes in this code and you will understand what I have done so after this statement that is return rapper okay let me clear all this I can just write at the rate function number one and now I'll just Define my next function that is function number two and over here I'll just print pythonista and and now when I call my function number two the output is going to be same so as you can see the output is same which is hello pythonista welcome to python Eda tutorial so what I have changed here is I have changed this over here so I've have use this P syntax or you can call it a syntactic sugar as well it makes your job easier so this is how you can use a simple decorator in your functions guys so now let's try to understand the concept of decorators in Python a few more examples so I'm going to take a program inside which I'm going to specify a decorator with arguments so I'll just take function number one and inside this I'm going to pass function again now I'm going to Define my rapper function inside which I will have arguments so earlier I didn't have arguments over here but now I'm going to have arguments inside this decorator so I'm I'm going to print hello again like I did in the last program and I'm going to call the function again so inside this I'm going to use arguments as well and after this I'm going to print the same statement that was welcome to Ed Python tutorial and I will return raer after this I will use the syntactic sugar function number one I'll write and after this I'll Define my function number two and over here I'll write the print statement let's say all right we can use a argument over here as well and we'll use the string interpolation again yeah when I print function number two I'm going to specify a name as well let's say was seene now my output is okay we have a error which is function one is is not defined so basically this we have made a mistake over here now it should work fine so we have hello Wasim welcome to Eda Python tutorial so this is a very simple example guys so we have actually used arguments in our decorator let's take a look at the next function that we have so I'm going to use a function in which I'm going to return values from a decorated function so I'll just Define a function function number one and inside this I'll pass function again and now I'll Define a rapper function with the a few arguments let's say and after this it's going to work the same way like we did so I'm going to write print let's say it worked so it will show us that it worked I'll return rapper and after this I will have that same syntactic sugar function one and I'll Define my function number two here pass name over here and I'll write print string interpolation get name and now when I print let's say function number two with name let's say python so what is the output that we are getting it's showing it worked so now that we are through with the decorator examples let's talk about fancy decorators in Python they're nothing but the complex features of decorators in Python and to explain this I'm going to take a few examples like class decorator and let's talk about them one by one so we're making a reference here so that we can use it for various purposes in the future as well so we not using the parenthesis over here because we're making a reference to this function so I'll clear this up and we'll talk about the class decorators now so there are two ways to decorate a class in Python the first one is where you can decorate the methods inside a class and there are built-in decorators like class method static method and property in Python so class method and static method Define methods inside a class that is not connected to any other instance of a class and property is normally used to customize the Getters and Setters of a class attribute so let's take an example to understand this so I'll take a class I'll make it more relatable so I'll not use functions instead I'll use let's say square and for my class over here I'm going to Define few functions so first of all I'm going to Define an init function and inside of self I'm using one more variable that is side now self do side is equal to side and I'm going to add a property over here so this is going to be my decorator guys so this is going to be my decorator it's a built-in operator guys I'll show you what it does so I'm going to Define one more function named as let's let's say side and inside this I'm going to pass self and now again I'm going to return self side and I'm going to use one more so this is my set of function guys and now inside this I'm going to use the side function and after this I'm going to use the value so if value is greater than equal to zero I going to get the side is equal to Value else I'm going to print that there is one arrrow over here and now again I'm going to use property and over here I'm going to Define area self again and inside this I'm going to return the area so I'm going to use self do side and I'm sure everyone must be familiar with what is the area of a square that is side Square so I'm using a double exponentiation operator over there which is used to calculate the square so if I make it as three it's going to be a q but we don't need that so I'm just going to leave it at two now I'm going to define a class method and it is going to have one more function let's say unit square and inside this let's have one more variable CLS and now I'm going to return one we done with the so we are done with the class which has all these functions and built-in class decorators like property class method and Setter and getter all those so I'm going to have square over here I'm going to specify the side as five now let's say what my side is yes and I'm going to print the area as well so when I do this my output is 5 and 25 now sometimes it's useful to have a decorator that can keep a track of state so let's take a few more examples to explain decorators in Python in detail so I'm going to make a Singleton class using class decorators so first of all I'll import fun tools and after this I'm going to define a Singleton class so name is as Singleton now after that I am going to use the function tools do wraps inside this CLS now comes the wrapper function and inside this I'm going to have a few arguments as well and after this I'm going to get the instance is equal to CLS ORS and K I'm going to return rapper again making a reference to the function and not calling it but I'm going to use this to make an rapper dot instance okay we making a small Arrow here now I'll just write Raper do instance is equal to none now I'm going to return rapper again after this I have a single T and after this I'll have class one I'm going to pass and let's say first is equal to 1 and let's say second is equal to one as well and I'm going to print first is second so let's see if we get true or false are we getting a error guys all right I have made a mistake over here I had to add a if statement that's why we're getting this error guys and after this uh it should work fine now so it is actually true and we know that our Singleton class only has one instance and there are plenty of singl ton in Python including true none Etc so now that we are done with making a singlet ton class I want to talk about nesting decorators so in a function you can actually use nested decorators as well so I'll show you the syntax for that so basically what you can do is you'll just write function one and you can write function two but you have to Define all those before that you use after that you can just Define a function name and print whatever you want you can use multiple decorators by stacking them on top of each other and now let's take an example in which I'm going to take arguments in a decorator so for that I'm going to import function tools and after this I will Define a function let's say repeat and and inside this I'll write number now again I'll write one more function let's say decorator repeat and after this I will pass a function inside this and now I will make one decorator let's say fun tools wraps inside this I will pass function and I'll Define one more W function over here and inside this I will pass a few arguments now for in range number value is equal to I'm going to return value after this and return wrapper making not using the parenthesis again and after this I'm going to return Deco RoR repeat and again not using the parenthesis now we make our decorator let's say repeat inside this I'll specify the number itself let's say five after this I'll Define a function and inside this I'll pass name using the string interpolation we will have a name again so let's just say I want to print my name again or I can use python as well so I'll just write python over here now when I run this there should not be any errors so I'm getting it as python as four times so instead I can use four over here I'll get it four times so this is my repeat function so I'm using it as an argument two times also we can use it for 20 times as well so it is always useful to pass an argument in a decorator and now that we have come to the end of the session I hope the concepts covered in this tutorial are clear to you guys and if you have any questions you can mention them in the comments and don't forget to like share and subscribe to Eda for more exciting tutorials and also press the Bell icon to get the latest updates from EDD Rea thank you