Python class special methods or magic methods

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:

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

The article was originally published at MicroPyramid blog