OOP in Python notes.txt

OOP in Python =

1 Class and objects in the Class

stack implementation using list

2. static method => without creating instance in the Class
use @classmethod

example =>

class A:
    @classmethod
    def squareIt(self, x):
        print(x * x)

A.f(3)

class B:
    @staticmethod
    def squareIt(x):    #No self keyword in cse of static method
        print(x * x)    

B.f(3)

3. Inheritance = Is a relationship then Inheritance

class BaseClass:
    def walk(self):
        print("I am walking)

class DerivedClass(BaseClass):
    pass

d = DerivedClass()
d.walk()    # will work fine

Multple Inheritance is supported in Python

4. Polymorphism

Many forms. Multlple class can have same methods

5 Properties 
virtual attributes in the class. 

self._name = name
use @property for only getter methods. There shoud not be any setters.  

6. Operator Overloading
 
 Which allows same operator to have different meaning accpording to the context
 + performs differently in case of numbers, list and string.
 Operaor overloading can be implemented by defining the magic method.

+ __add__(self, other)
- __sub__(self, other)
* __mul__(self, other)
/ __truediv__(self, other)
// __floordiv__(self, other)
% __mod__(self, other)
** __pow__(self, other)

__lt__(self, other)
__gt__(self, other)

e.g. Vector addition
class A:
    def __init__(self, a,b):
        self.a = a
        self.b = b

    def __add__(self, other):
        return self.a +other.a, self.b + other.b

obj1 = A(1,2)
obj2 = A(3,4)

print(obj1 + obj2)

7. Metaclass in Python
Everything is object in Python

type(4)
class 'int'

Metaclass is class of class
default metaclass is type.

Metaprogrammng

class VrboseMetaClass(type):
    def __new__(cls, class_name, class_parents, class_dict):