What methods are available in Python classes?

In Python, classes can have the following types of methods:

1. Instance Methods Take self as the first argument (a reference to the class instance). They work with attributes of a specific instance.

   class MyClass:
       def __init__(self, value):
           self.value = value
   
       def print_value(self):
           # Working with the instance attribute
           print(f"Value: {self.value}")
   

2. Class Methods Take cls as the first argument (a reference to the class itself). Declared with the @classmethod decorator. They can be used as alternative constructors or to access class attributes.

   class MyClass:
       class_variable = "Class Data"
   
       @classmethod
       def print_class_variable(cls):
           # Working with the class attribute
           print(f"Class Variable: {cls.class_variable}")
   
       @classmethod
       def from_string(cls, data_string):
           # Alternative constructor
           value = int(data_string.split(":")[1])
           return cls(value)
   

3. Static Methods Do not take self or cls. Declared with the @staticmethod decorator. They do not have access to instance or class attributes and are used to group related functions within a class where access to class or instance state is not needed.

   class MyClass:
       @staticmethod
       def helper_function(x, y):
           # Independent function conceptually related to the class
           return x + y
   

4. Special Methods (Dunder Methods) Have names starting and ending with double underscores (e.g., __init__, __str__, __len__). Used to define class behavior with built-in functions and operators.

   class MyList:
       def __init__(self, items):
           self.items = items
   
       def __len__(self):
           # Defines behavior of len()
           return len(self.items)
   
       def __str__(self):
           # Defines string representation of the object
           return f"MyList with {len(self.items)} items"
   

Summary table:

Method Type	First Argument	Decorator	Access to State	Typical Purpose
Instance Method	self	No	Instance	Working with specific object data
Class Method	cls	@classmethod	Class	Alternative constructors, access to class attributes
Static Method	None	@staticmethod	None	Helper functions, independent of state
Special Method	Depends on method	No	Instance/Class	Overriding operations and built-in functions