List of python class special methods or magic methods

In this blog posts lets discuss about using magic methods/special methods in python development

What happens when we create an object in python class?

class Address(object):
    def __init__(self, city, pin): = city = 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)
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

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)
             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

Posted On 27 January 2017 By MicroPyramid

About Micropyramid

Micropyramid is a software development and cloud consulting partner for enterprise businesses across the world. We work on python, Django, Salesforce, Angular, Reactjs, React Native, MySQL, PostgreSQL, Docker, Linux, Ansible, git, amazon web services. We are Amazon and salesforce consulting partner with 5 years of cloud architect experience. We develop e-commerce, retail, banking, machine learning, CMS, CRM web and mobile applications.

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