In this blog posts lets discuss about using magic methods/special methods in python development
class Address(object):
def __init__(self, city, pin):
self.city = city
self.pin = pin
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.
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
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