Is 'self' Keyword Mandatory Inside The Class Methods?

I am python Begineer and i learned that first parameter inside the method should be contain some 'self' keyword but i found the following program runs without self keyword can you

Solution 1:

Code you've posted has indentation errors within it, you should first indent methods and it's content, meaning that, methods are within class. On the other hand, self refers to instance, which calls specific method and gives access to the all instance data. For example

student1 = Student('name1', 20)
student2 = Student('name2', 21)
student1.some_method(arg1)

in the last call, behind the scenes student1 is passed for self parameter of the method, meaning that all student1's data is available through self argument.

What you are trying is to use staticmethod, which has no data of the instance and is aimed to logically group class related functions without explicit instance, which does not require self in method definition:

classStudent:
  ...
  @staticmethoddefget_biggest_number(*ages):
    # do the task here

On the other hand, if you would like to track all student instances and apply get_biggest_number method automatically work on them, you just have to define class variable (rather than instance variable) and on each instance __init__ append new instance to that list:

classStudent:
  instances = list()  # class variabledef__init__(self, name, age):
    # do the task
    Student.instances.append(self)  # in this case self is the newly created instance

and in get_biggest_number method you just loop through Student.instances list which will contain Student instance and you can access instance.age instance variable:

@staticmethoddefget_biggest_number():
  for student_instance in Student.instances:
    student_instance.age  # will give you age of the instance

Hope this helps.

Solution 2:

You shouldn't mistake classmethod with instance methods. In python you can declare a method inside a class as classmethod. This method takes a reference to the class as the first argument.

classStudent(object):
    def__init__(self,name,age):
        self.name = name
        self.age = age

    defget_biggest_number(self, *age):
        result=0for item in age:
            if item > result:
                result= item
        return result

    @classmethoddefget_classname(cls):
        # Has only access to class bound items# gets the class as argument to access the classreturn cls.__name__

    @staticmethoddefprint_foo():
        # has not a reference to class or instanceprint('foo')

Solution 3:

self in python refers to the instance of the class that is created. Something like this in C# and Java. However there's some differences but in short: when you don't use self as input of a method, actually you're saying that this method does not need any instance, that means this method is a static method and will never use any of class attributes.

In your example we can call get_biggest_number method with not even one instance, for example you can call this method just like this:

Student.get_biggest_number(20,30,43,32)

and the output will be 43.

Solution 4:

The self keyword is used to represent an instance (object) of the given class. ... However, since the class is just a blueprint, self allows access to the attributes and methods of each object in python.

classClassA:defmethodA(self, arg1, arg2):
        self.arg1 = arg1
        self.arg2 = arg2

let say ObjectA is an instance of the class.

Now when ObjectA.methodA(arg1, arg2) is called, python internally converts it as:

ClassA.methodA(ObjectA, arg1, arg2)

The self variable refers to the object itself and the code becomes as:

classClassA:

    def methodA(ObjectA, arg1, arg2):
        ObjectA.arg1 = arg1
        ObjectA.arg2 = arg2