Python: class vs. instance vs. static methods

In Python, a method provides functionality to a Class.

There are, broadly, three types of methods:

Class Methods : Provide functionality to a class itself
Instance Methods : Provide functionality to one instance of a class
Static Methods : Provide functionality that can be accessed from a class or from one instance of a class

Consider the following Python class, which defines a Person object and the methods which allow that object to say "hello":

class Person():
  # (Discussing __init__ is beyond the scope of this
  # tutorial)
  def __init__(self, first_name):
    self.first_name = first_name

  # Instance methods are the default method type in a
  # class definition. They receive the class instance
  # itself as their first argument. By convention, 
  # the parameter for this argument is labeled 'self'.
  def say_hi_from_an_instance(self):
    print(f"Hello! My name is {self.first_name}.")

  # Class methods are defined using a special
  # decorator, and receive the class as the first
  # argument. By convention, the parameter for this
  # argument is labeled 'cls'.
  @classmethod
  def say_hi_from_the_class(cls):
    print(f"Hello! I am a {cls.__name__}.")

  # Static methods are defined using a special
  # decorator. They are available on the class and on
  # instances of the class.
  @staticmethod
  def say_hi_from_anywhere():
    print("Why, hello!!!")

Now, from the class:

# We can call the class method greeting
> Person.say_hi_from_the_class()
Hello! I am a Person.

# But we cannot call the instance method greeting
> Person.say_hi_from_an_instance()
Traceback ...
TypeError: say_hi_from_an_instance() missing 1 required positional argument: 'self'

While, from an instance of the class:

> a_person = Person('Louise')

# We can call the instance method greeting
> a_person.say_hi_from_an_instance()
Hello! My name is Louise.

# And we can still call the class method greeting
> a_person.say_hi_from_the_class()
Hello! I am a Person.

Static methods are available on both classes and class instances. They are intended to provide functionality that does not rely on the class or instance itself:

> Person.say_hi_from_anywhere()
Why, hello!!!
> a_person.say_hi_from_anywhere()
Why, hello!!!

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Python: class vs. instance vs. static methods

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