Why are "self" and "cls" interchangeable as the first argument in class and instance methods?

Question

I understand from the question "Difference between 'cls' and 'self' in Python classes?" that cls is used in class methods, whereas self is used in instance methods.

However, I used self in class methods and it is still working fine.

For example,

class Test:
  
  @classmethod
  def hello(self, name):
    print ('hello '+name)

Test.hello('Tom')

What, exactly, does cls or self do in class methods?

Answer 1

You can use any name you want. But as per the naming standard defined within PEP 8 (Style Guide for Python Code), it's better to name self for the first argument to instance methods and cls for the first argument to class methods.

Function and Method Arguments

Always use self for the first argument to instance methods.

Always use cls for the first argument to class methods.