# 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](https://docs.python.org/3/reference/datamodel.html#special-method-names).

```python
# 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
```