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Hello welcome to this tutorial on class methods and static methods in order to understand these two

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methods.

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We will look at an example so here we have a library class and this glass contained a class attribute

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books so the class variable books is basically a list of items or list of Titan's now coming to the

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init method in the index method.

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We have defined two parameters the student I.D. title of the book and then we initialize these two arguments.

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The student I.D. and the title of the book.

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Next we have two methods in this class.

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One is the detailed method and the other is update list method.

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Many details method is called using an instant.

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It returns the student I.D. That is to whom the book is issued and the title of the book issued.

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Next update list method once a book is issued.

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It needs to be removed from the list of available books in the library and the method update list does

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that in order to issue books.

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I need to create an instance of the class library and calling the instance method using the instance.

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Will you give me details of the transaction.

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That is it gives me details such as the student I.D. and the title of the book and also update the collection

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of the books in the library in order to access these instance variables the student I.D. the title and

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the list of books available in the library.

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I need to first have an instance so an object needs to be created first and then we can call instance

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methods using this object.

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Now let us say we want to add more books to the collection in the library and to do this.

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I do not need to create an instance of the class first so I need to update the list of books.

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In the class attribute and for that I do not need to create an instance.

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So say for example you will create an instance.

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Eric and me will pass the parameters say the student I.D. is 1 2 3 4 and then the title of the book

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that is available in the collection in the library is 8.

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Now I have another requirement.

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I want to add more books to the collection and the library and in order to do this I don't need to create

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an instance of the class first.

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So that means I want to update the list or the class variable books and for that in order to do this

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I do not need any instance of an object in order to update this list.

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So I want to keep adding books to the collection without having to create an instance.

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And this is possible using class methods.

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Here is the class method.

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Add to list and to this method we have parsed two parameters.

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One is to see a list parameter which means see a list means the class and then we have another list

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as a parameter.

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A list of books and in this method we are concatenate thing the new list to the old list and then returning

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the new list of books for the instance.

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Methods like details method and the update list method we have past self as the parameter and self refers

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to the instance of a class when the method is gone.

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When we pass see a list as a parameter to the method the parameter C is points to the class and not

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the object instance when the method is called.

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So we do not need to create an instance before calling class methods so class methods are not bound

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to an object or an instance but they're bound to a class so we pass the first parameter as seamless

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and non self and class method.

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Also useful for defining alternate constructors meaning the main constructor of a class is defined in

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the init method.

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So another example we have these two parameters defined in the input method coming to the class method

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actor list it takes two parameter d see a list parameter and the other is new collection which contains

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a list of books that are to be added to the collection in the library.

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Using the class method actor list we have defined a new constructor a new set of parameters have been

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defined using this class method.

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And Python only allows one init method but class so using class method.

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It is possible to add as many alternate constructors as necessary in order to be able to use a method

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as a class method.

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We need to mark the method with a decorator like this

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and a decorators have to immediately proceed a method or a function and they start with the add sine

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unlike the instance methods coming to the instance method.

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We do not need to have any decorator any method that we create in a class will automatically be created

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as an instance method unless we tell Python otherwise.

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And here is the class library.

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So let's go ahead and execute this.

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And in this class library we have.

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As discussed we have a class attribute books and a constructor the init method.

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And apart from this we have to instance method.

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Both of these instance methods.

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Take one parameter self which bind to an instance of the class library.

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The new method is called so we have discussed that class method are bound to the class and not an instance

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that has instant methods are bound to the instance so let us try calling the the instance method without

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creating an instance in the first place.

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So let us see what will happen.

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Letters call the instance method transaction using the class library and it does not take any parameters

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apart from the self parameter.

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Let's execute this line.

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So here we have the unbound method transaction must be called with an instance of the class as the first

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argument so without creating an instance of the class library we can not execute or call the method.

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The Instance methods that are defined in the class so we have not yet defined an instance.

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Now coming to class method add to list class methods as we have discussed before and methods that are

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not bound to an object but an instance.

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But they are bound to a class

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so class method deal with class itself this means we can use the class and it attributes inside this

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method rather than dealing with a particular instance

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and in order to use the method actor list as a class method we have decorated this class with this add

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class method decorator Noda to flag it as a class method and took this class method the first parameter

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that we have passed is C S and this bind to the class and A.D. object instance as we have discussed

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before.

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So let us try calling this class method using the class itself

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so library da add to this and to this method we will pass a list

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of books C we will pass in by J K just like we do not pass any values to the self parameter in case

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of instance method we do not have to pass a new value to the C a list parameters.

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Python does it for us automatically so let's call this method I do list using the class library and

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then execute so hard as the output.

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So these are the items that I have been on the books that have been added to the collection.

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And this is of a new collection of books that are available in the library.

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So without even creating an instance we have changed the state of the class and now in order to call

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the instance methods letters create an instant C the instant is Eric student I.D..

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And the title of the book is C..

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B let's pass these two arguments to the class library and execute.

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Eric is an object or an instance of the library class.

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Now we can now go ahead and call the instance methods using this instance.

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Eric so that a dot transaction so here we have the output from the instance method transaction.

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Let's call the second method.

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Update list and after removing the book that has been issued to the student.

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This is the updated list.

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So we have talked about class method which are bound to a class itself and not to any instance of a

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class coming to static methods a static method is a method that knows nothing about the class or the

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instance it was called on.

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So Biden doesn't have to instantiate a bound method for an object.

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And also we do not have to parse the parameters clause or save as implicit first arguments do a static

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method.

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So let us see an example.

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In the class library we have added another method known as a static method.

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So where you have decorator the method issued by using the at static method decorator.

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And if you observe we have not parsed the self parameter which points to an instance or the class parameter

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which bind to a class object to this static method.

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So a static method knows nothing about a class or an instant but it just deals with these parameters

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that we have past so static method can neither access the instance did not the class state the work

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like regular functions but they belong to the classes namespace and when do we need to define static

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method in a class.

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So for example when we need some functionality which is not with reference to an object but with reference

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to the complete class we can define a static method.

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Say for example when we need a functionality that doesn't access any property of a class but makes sense

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that it belongs to the class we use static methods.

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So here in this example I have defined the static method issued by.

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And this takes an amateur name.

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Let us change this to library an undisclosed name and add this function displays the name of the librarian

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who issues the book within this particular function.

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We are not accessing any of the properties of a class not changing the state of a class or an instant.

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So let execute this and you can call the static method using the class so here we have called the issued

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by static method using the class library.

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And when we execute this the print function displays this message.

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So this type of method takes needed a self or not a class parameter but it can accept arbitrary number

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of other parameters.