python class special methods or magic methods

Reading Time : ~ .

What happens when we create an object in python class ?

class Address(object):
    def __init__(self, city, pin):
        self.city = city 
        self.pin = pin
creating instance of the object
a = Address("hyderabad", "500082")

before creating the instance of the class "__new__" method will be called. This method takes  parameter "class", "args", "kwargs" and  It will bind the data type to given class. After it will call the "__init__" method with arguments and keyword arguments.

>>> a = Address.__new__(Address)
>>> type(a)
__main__.Address
>>> a.city
AttributeError: 'Address' object has no attribute 'city'
# object created but not initialised that's the reason we get error
>>> a.__init__("hyderabad", "500082")
# now we can access the attributes
>>> a.city
'hyderabad'

we can cosider bilt-in methods of an object as magic methods. We can also override the built-in methods functionality.

list of magic methods:

Binary Operators

Operator           Method
+                       object.__add__(self, other)
-                        object.__sub__(self, other)
*                        object.__mul__(self, other)
//                       object.__floordiv__(self, other)
/                        object.__div__(self, other)
%                      object.__mod__(self, other)
**                      object.__pow__(self, other[, modulo])
<<                     object.__lshift__(self, other)
>>                     object.__rshift__(self, other)
&                       object.__and__(self, other)
^                       object.__xor__(self, other)
|                        object.__or__(self, other)

Assignment Operators:

Operator          Method
+=                     object.__iadd__(self, other)
-=                      object.__isub__(self, other)
*=                      object.__imul__(self, other)
/=                      object.__idiv__(self, other)
//=                     object.__ifloordiv__(self, other)
%=                    object.__imod__(self, other)
**=                     object.__ipow__(self, other[, modulo])
<<=                   object.__ilshift__(self, other)
>>=                   object.__irshift__(self, other)
&=                     object.__iand__(self, other)
^=                      object.__ixor__(self, other)
|=                      object.__ior__(self, other)

Unary Operators:

Operator          Method
-                       object.__neg__(self)
+                      object.__pos__(self)
abs()                object.__abs__(self)
~                      object.__invert__(self)
complex()        object.__complex__(self)
int()                  object.__int__(self)
long()               object.__long__(self)
float()               object.__float__(self)
oct()                object.__oct__(self)
hex()               object.__hex__(self)

Comparison Operators

Operator          Method
<                      object.__lt__(self, other)
<=                    object.__le__(self, other)
==                    object.__eq__(self, other)
!=                     object.__ne__(self, other)
>=                    object.__ge__(self, other)
>                      object.__gt__(self, other)

Let's take an example to override the functionality "+" [__add__] operator

class Vector(object):
    def __init__(self, *args):
        """ Create a vector, example: v = Vector(1,2) """
        if len(args) == 0:
             self.values = (0,0)
        else:
             self.values = args

    def __add__(self, other):
        """ Returns the vector addition of self and other """
        added = tuple(a + b for a, b in zip(self.values, other.values) )
        return Vector(*added)
now use the "+" operator with two vectors
>>> v1 = Vector(1, 2)
>>> v2 = Vector(10, 13)
>>> v3 = v1 + v2
>>> v3.values
(11, 15)

When statement "v3 = v1 + v2 " executes "__add__"  is called and it returns a new Vector object.

for more information please visit the python docs

    By Posted On
SENIOR DEVELOPER at MICROPYRAMID

Need any Help in your Project?Let's Talk

Latest Comments
Related Articles
Programming with python: Descriptors Ramya Ambati

Python descriptors are object attributes that are only invoked for new style of classes. Python descriptors comes under the category of meta programming(code that manipulates ...

Continue Reading...
FABRIC – LEARNING PART 2 Ashwin Kumar

Using Fabric, we can develop interactive script for ec2 region, ec2 flavour amazon web services. For this, you need aws account, security group, key pair, ...

Continue Reading...
Python to Debian package: Simple, Easy and Fast Dinesh Deshmukh

Packaging python script to debian follows strict instructions, using the following instructions, most of the steps can be skipped hence making it easy and fast.
Continue Reading...

Subscribe To our news letter

Subscribe to our news letter to receive latest blog posts into your inbox. Please fill your email address in the below form.
*We don't provide your email contact details to any third parties