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Magic/Dunder Methods in Python

 


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Magic/Dunder Methods in Python

Magic methods, also known as dunder (double underscore) methods, in Python are special methods that begin and end with double underscores. They allow the customization of the behavior of built-in Python operations for user-defined classes.

Common Magic Methods

1. __init__

Initializes a new instance of a class.


class Person:
    def __init__(self, name, age):
        self.name = name
        self.age = age

person = Person("Alice", 30)
print(person.name)  # Output: Alice
print(person.age)   # Output: 30

2. __str__

Returns a string representation of the object.


class Person:
    def __init__(self, name, age):
        self.name = name
        self.age = age

    def __str__(self):
        return f"Person(name={self.name}, age={self.age})"

person = Person("Alice", 30)
print(person)  # Output: Person(name=Alice, age=30)

3. __repr__

Returns an unambiguous string representation of the object, often one that could be used to recreate the object.


class Person:
    def __init__(self, name, age):
        self.name = name
        self.age = age

    def __repr__(self):
        return f"Person(name='{self.name}', age={self.age})"

person = Person("Alice", 30)
print(repr(person))  # Output: Person(name='Alice', age=30)

4. __add__

Defines the behavior of the addition operator + for the objects of the class.


class Vector:
    def __init__(self, x, y):
        self.x = x
        self.y = y

    def __add__(self, other):
        return Vector(self.x + other.x, self.y + other.y)

v1 = Vector(2, 3)
v2 = Vector(4, 5)
result = v1 + v2
print(result.x, result.y)  # Output: 6 8

5. __len__

Defines the behavior of the len() function for the objects of the class.


class MyList:
    def __init__(self, items):
        self.items = items

    def __len__(self):
        return len(self.items)

my_list = MyList([1, 2, 3])
print(len(my_list))  # Output: 3

Other Dunder Methods

  • __getitem__, __setitem__, __delitem__: Indexing operations
  • __iter__, __next__: Iterator protocol
  • __call__: Callable objects
  • __eq__Defines the functionality of the equality operator
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