Python Decorators Tutorial

dear friends we are going to look at decorators in Python today now when you read about decorators online it sounds like a complex concept but it's really not that complex and the goal of this tutorial is to explain decorators in a very simple easy way ok so the way we are going to start this tutorial is first let's discuss what problem decorators will try to solve right like what is really the need of decorators here I have two functions calculate square and calculate cube and what these functions are doing is for example let's look at this function first this function is taking an array of numbers as an input it's just I trading through the array and calculating the square of that number and putting that into a result calculate cube does the same thing but instead of square it is calculating a cube ok very very easy functions and here I am calling those functions for a range of 1 to this number now often you have a need of measuring the performance of a function and by performance I mean how much time does every function take to execute and in order to measure the timing you have to use the time module I mean this is one of the ways I usually like to do that where I will take the start time so what this will do is when function execution at is at this point it will take the start time and once you are done you will take the end time and here you will say calculate square toke how much did it take so it takes an - start in 2000 so this will give you a result in seconds and I am multiplying it by thousand just to produce a result in millisecond so this will say okay it took this many millisecond alright and we do the same thing for this function because you want to measure the performance of both of these functions okay okay and I'm calling these functions here down below okay pretty straightforward when I run the program I see the performance that the first function took 14 milliseconds the second one took 19 now the problem with this code is that let's say you have a complex software project when you have but returned 200 functions so in in order to measure the performance of all those 200 functions you have to write the start time end time the exactly same line of code in every function now this is not good you see like these lines are getting repeated start and both of these lines are getting repeated in every function that you want to measure the performance second problem is that there is a logic in this function now that logic is combined with the timing logic okay so the main logic of this function is to calculate square now you are cluttering that logic with the timing code and it makes code less readable there has to be a better way of doing this and that better way is basically decorator so decorator allows you to wrap your function in another function so let me show you how you do that so first I am going to remove this timing code all right so this is purely a timing code which I am removing and I want to have a function which has just the logic that that function is supposed to do so this function looks now much clean so in order to do decorator first you need to define the wrapper function so I'm going to call my wrapper function time it and that wrapper function will take function as an argument now functions are first class objects in Python what I mean by that is you can pass function as an argument to a function you can return function as a return value from another function okay you will understand this as we continue writing our code so in this function I'm going to define another function okay and call it a wrapper so notice that Python allows you to write nested function so you can have one function inside another function and what this function is doing is it is taking the positional arguments which is your star ARBs and your keyword arguments and then it will start the timer here and then it will call the function that was passed as an argument so I'm going to call function here with argument and keyword argument and then I will measure the end time and in the end you will say function dot underscore new score name so this underscore underscore name will return you the name of that function okay and this function took how much it took and - start so this piece of code is same as what we wrote before you want to measure the time of function in millisecond that's why you are doing this okay and of course you want to return the result all right and what so he this is my inner function okay and here my function ends and at this point I want to return this wrapper function here so again I'm returning a function from another function that's why this function is called a first-class object you can treat it just like your normal variable you can return it you can pass it as a function argument and so on okay so let's let's first run the program and I will give you more details on on this time it function okay so let's run it okay so it looks like there is a problem oh yeah I forgot to decorate it so I created this timing function now what you need to do is decorate these other functions okay so the syntax is you have to say add so before this function line just say at and just say time it okay [Music] cool so you can see that now it is saying calculate Square to this many millisecond and calculate you took this many millisecond so you see the beauty now that any function that you want to measure performance off now once you have defined this code you can just put this tag at the beginning and it's gonna measure the performance so this is really good it makes this code much more readable and then all your timing core is restricted into one function okay now I'm going to show you how all of this actually walked by debugging it I have put a breakpoint here in this function in my pym I will start my debugging session okay so not in order to go inside I will place f11 so when you do this you notice that when it called calculate square function it it didn't it didn't go to here at the first line of this function because it realized that this function is decorated it needs to call time it first because time it is a wrapper so it went here and from here you can just do f10 to go to the next line now here this funk is actually calculate square so when you go inside that you notice that now the flow is coming here okay so it will go here then eventually it will come to result okay you can see that it calculated the result it's here and then when you press next you see it came back here f10 span so again it is here and f10 okay so you now kind of get an idea on how it all worked cool so again just to recapture the main highlights decorator acts as a wrapper to your original function and it and you can do things like timing your function or even logging certain lines at the beginning and end of the function so these are like some of the commonly used cases of using decorators so I hope you guys had a fun time learning decorators and I hope that I have made it little simple if you have any question please don't hesitate to put it in the comments box below thank you for watching

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Keywords: python decorators, python decorators tutorial, python decorators explained, decorators in python, decorators tutorial, python decorators simple example, python decorator, decorator in python, decorators, decorator

Id: nYDKH9fvlBY

Length: 10min 24sec (624 seconds)

Published: Mon Dec 19 2016