Dunder or magic methods in python

Dunder methods (also called magic methods) are special methods in Python that allow us to define how objects behave with built-in operations. These methods are identified by double underscores (__) as prefix and suffix, like __init__ or __str__.

Basic Object Representation

Without defining custom string representation, Python objects display their memory location ?

class String:
    # magic method to initiate object
    def __init__(self, string):
        self.string = string

# object creation
my_string = String('Python')
# print object location
print(my_string)

<__main__.String object at 0x000000BF0D411908>

Using __repr__ for String Representation

The __repr__ method defines the "official" string representation of an object ?

class String:
    # magic method to initiate object
    def __init__(self, string):
        self.string = string
    
    # print our string object
    def __repr__(self):
        return 'Object: {}'.format(self.string)

# object creation
my_string = String('Python')
# print object representation
print(my_string)

Object: Python

Adding Custom Operators with __add__

Without defining __add__, trying to use the + operator will raise an error ?

class String:
    def __init__(self, string):
        self.string = string
    
    def __repr__(self):
        return 'Object: {}'.format(self.string)

my_string = String('Python')
try:
    print(my_string + ' Programming')
except TypeError as e:
    print(f"TypeError: {e}")

TypeError: unsupported operand type(s) for +: 'String' and 'str'

Implementing __add__ Method

The __add__ method enables the + operator for our custom class ?

class String:
    def __init__(self, string):
        self.string = string
    
    def __repr__(self):
        return 'Object: {}'.format(self.string)
    
    def __add__(self, other):
        return self.string + other

# object creation
my_string = String('Hello')
# concatenate String object and a string
print(my_string + ' Python')

Hello Python

Common Dunder Methods

Conclusion

Dunder methods provide a powerful way to customize object behavior in Python. They enable your custom classes to work seamlessly with built-in functions and operators, making your code more intuitive and Pythonic.