Short Notes on Python - OOPS

OOPs - Definitions

  • Class - is a template model for creating classes.
  • Class Variables - variables shared by all object
  • Instance Variables - variable specific to a object, gets created during object creation
  • Data members - Class/Instance Variables - that hold some data related to that class
  • Method - A special function related to a class.
  • Instance - an individual object of a class.
  • Instantiation - the task of creating an instance of a class

  • Object - A uniq instance of a data structure that is defined by a class. This contains 1. Data Members(Instance & Class variables) 2. Methods

  • Operator Overloading - the assignment of more than one function to a particular operator.

  • Inheritance - transfer of characteristics of a class to other class that its derived from it.

  • Class Variables are accessed as «class_name».«class_variable_name»

OOPs - way of working with variables

  • getattr(obj, name[, default]) - to get a variable from an obj
  • hasttr(obj, name) - return True/False - to check if the obj has a variable
  • setattr(obj, name, value) - setting a new value to a obj’s attribute
  • delattr(obj, name) - deleting the obj variable

OOPs - Built in Class Attributes

  • dict - contains class name space
  • doc - class documentation
  • name - class name
  • module - module name which that this object’s class
  • bases - empty tuple/order of occurrence of its base class list

Destroying Objects (Garbage Collection)

  • When an object’s reference count reaches zero, Python collects it automatically.

Class Inheritance

  • A child class can also override data members and methods from the parent
  • Functions - issubclass() or isinstance() are used to check a relationships of two classes and instances.

Data Hiding

  • attributes with a double underscore prefix

Magic Functions/ Dunder methods

  • init - constructor
  • repr - representation for developer(prefer to show case all contructor variables)
  • str - print output for a object(generic, more user friendly to read)
  • add - you can add objects
  • len - you can create a lenght of the object

others

  • @property - converts a method to be accessed as a variable
  • @<property-variable>.setter - helps you assign a variable to a property
  • @<property-variable>.deleter - helps you delete a variable to a property
class Employee:

    def __init__(self, first, last):
        self.first = first
        self.last = last

    @property
    def email(self):
        return '{}.{}@email.com'.format(self.first, self.last)

    @property
    def fullname(self):
        return '{} {}'.format(self.first, self.last)

    @property.setter
    def fullname(self, name):
        self.first, self.last = name.split(' ')

    @property.deleter
    def fullname(self):
        self.first, self.last = None, None
        print('Delete Name !')

emp_1 = Employee('John', 'Smith')

print(emp_1.first)

# Note: email is a property
print(emp_1.email)
print(emp_1.fullname)

# Note: using property 
emp_1.full_name = 'Adon Hoe'
print(emp_1.fullname)