Difference between cls and self in Python classes

Question

Why is cls sometimes used instead of self as an argument in Python classes   For example   class Person      def   init   self  firstname  lastname           self firstname   firstname         self lastname   lastname       classmethod     def from fullname cls  fullname           cls firstname  cls lastname   fullname split      1

User · Answer

This is very good question but not as wanting as question. There is difference between 'self' and 'cls' used method though analogically they are at same place

def moon(self, moon_name):
    self.MName = moon_name

#but here cls method its use is different 

@classmethod
def moon(cls, moon_name):
    instance = cls()
    instance.MName = moon_name

Now you can see both are moon function but one can be used inside class while other function name moon can be used for any class.

For practical programming approach :

While designing circle class we use area method as cls instead of self because we don't want area to be limited to particular class of circle only .

User · Answer

The distinction between  quot self quot  and  quot cls quot  is defined in PEP 8   As Adrien said  this is not a mandatory  It s a coding style  PEP 8 says   Function and method arguments  Always use self for the first argument to instance methods  Always use cls for the first argument to class methods

User · Answer

It s used in case of a class method  Check this reference for further details   EDIT  As clarified by Adrien  it s a convention  You can actually use anything but cls and self are used  PEP8

User · Answer

Instead of accepting a self parameter  class methods take a cls parameter that points to the class   and not the object instance   when   the method is called    Since the class method only has access to this cls argument  it can   t   modify object instance state  That would require access to self   However  class methods can still modify class state that applies across all   instances of the class    -Python Tricks

User · Answer

cls implies that method belongs to the class while self implies that the  method is related to instance of the class therefore member with cls is accessed by class name where as the one with self is accessed by instance of the class   it is the same concept as static member and non-static members in java if you are from java background

[python] Difference between 'cls' and 'self' in Python classes?

Examples related to python

Examples related to class

Examples related to object

Examples related to terminology

Examples related to self