Python special methods

In Python, special methods (also known as dunder methods) are a set of predefined methods that you can use to enrich your classes. They are also known as "magic methods" because they begin and end with double underscores (e.g. __init__).

These methods allow you to define the behavior of certain operations (such as addition, comparison, etc.) that are applied to your objects. For example, you can use the __len__ method to define the behavior of the len() function when it is called on an instance of your class.

Here is a list of some common special methods in Python:

Initialization and Construction Description

• __new__(cls, other) To get called in an object's instantiation.

• __init__(self, other) To get called by the __new__ method.

• __del__(self) Destructor method.

Unary operators and functions Description

• __pos__(self) To get called for unary positive e.g. +someobject.

• __neg__(self) To get called for unary negative e.g. -someobject.

• __abs__(self) To get called by built-in abs() function.

• __invert__(self) To get called for inversion using the ~ operator.

• __round__(self, n) To get called by built-in round() function.

• __floor__(self) To get called by built-in math.floor() function.

• __ceil__(self) To get called by built-in math.ceil() function.

• __trunc__(self) To get called by built-in math.trunc() function.

Augmented Assignment Description

• __iadd__(self, other) To get called on addition with assignment e.g. a +=b.

• __isub__(self, other) To get called on subtraction with assignment e.g. a -=b.

• __imul__(self, other) To get called on multiplication with assignment e.g. a *=b.

• __ifloordiv__(self, other) To get called on integer division with assignment e.g. a //=b.

• __idiv__(self, other) To get called on division with assignment e.g. a /=b.

• __itruediv__(self, other) To get called on true division with assignment

• __imod__(self, other) To get called on modulo with assignment e.g. a%=b.

• __ipow__(self, other) To get called on exponents with assignment e.g. a **=b.

• __ilshift__(self, other) To get called on left bitwise shift with assignment e.g. a<<=b.

• __irshift__(self, other) To get called on right bitwise shift with assignment e.g. a >>=b.

• __iand__(self, other) To get called on bitwise AND with assignment e.g. a&=b.

• __ior__(self, other) To get called on bitwise OR with assignment e.g. a|=b.

• __ixor__(self, other) To get called on bitwise XOR with assignment e.g. a ^=b.

Type Conversion Magic Methods Description

• __int__(self) To get called by built-int int() method to convert a type to an int.

• __float__(self) To get called by built-int float() method to convert a type to float.

• __complex__(self) To get called by built-int complex() method to convert a type to complex.

• __oct__(self) To get called by built-int oct() method to convert a type to octal.

• __hex__(self) To get called by built-int hex() method to convert a type to hexadecimal.

• __index__(self) To get called on type conversion to an int when the object is used in a slice expression.

• __trunc__(self) To get called from math.trunc() method.

String Magic Methods Description

• __str__(self) To get called by built-int str() method to return a string representation of a type.

• __repr__(self) To get called by built-int repr() method to return a machine readable representation of a type.

• __unicode__(self) To get called by built-int unicode() method to return an unicode string of a type.

• __format__(self, formatstr) To get called by built-int string.format() method to return a new style of string.

• __hash__(self) To get called by built-int hash() method to return an integer.

• __nonzero__(self) To get called by built-int bool() method to return True or False.

• __dir__(self) To get called by built-int dir() method to return a list of attributes of a class.

• __sizeof__(self) To get called by built-int sys.getsizeof() method to return the size of an object.

Attribute Magic Methods Description

• __getattr__(self, name) Is called when the accessing attribute of a class that does not exist.

• __setattr__(self, name, value) Is called when assigning a value to the attribute of a class.

• __delattr__(self, name) Is called when deleting an attribute of a class.

Operator Magic Methods Description

• __add__(self, other) To get called on add operation using + operator

• __sub__(self, other) To get called on subtraction operation using - operator.

• __mul__(self, other) To get called on multiplication operation using * operator.

• __floordiv__(self, other) To get called on floor division operation using // operator.

• __truediv__(self, other) To get called on division operation using / operator.

• __mod__(self, other) To get called on modulo operation using % operator.

• __pow__(self, other[, modulo]) To get called on calculating the power using ** operator.

• __lt__(self, other) To get called on comparison using < operator.

• __le__(self, other) To get called on comparison using <= operator.

• __eq__(self, other) To get called on comparison using == operator.

• __ne__(self, other) To get called on comparison using != operator.

• __ge__(self, other) To get called on comparison using >= operator.

There are many other special methods in Python, and you can find a complete list in the documentation.

# special_methods.py

class Book:
    def __init__(self, title, author, pages):
         """
         __init__ method. The method creates a new instance of a Book class.
         """
        print("A book is created")
        self.title = title
        self.author = author
        self.pages = pages

    def __str__(self):
         """
          __str__ method. This method should return an informal string representation of an object.
         """
        return "Title:{0} , author:{1}, pages:{2} ".format(
            self.title, self.author, self.pages)

    def __len__(self):
         """
          __len__ method. In our case, we print the number of pages of our book.
         """
        return self.pages

    def __del__(self):
         """
          The del keyword deletes an object. It invokes its __del__ method.
         """
        print("A book is destroyed")

book = Book("Inside Steve's Brain", "Leander Kahney", 304)

print(book)
print(len(book))
del book