Session 8 Python Programming slide series is part of Object-Oriented System Analysing & Designing in CS.QIAU Undergrad.

1. CS.QIAU - Winter 2020
PYTHONObject-Oriented - Session 8
Omid AmirGhiasvand
Programming

2. PROGRAMMING
IS A TYPE OF
IMPERATIVE PROGRAMMING PARADIGM
OBJECT-ORIENTED
Objects are the building blocks of an application

3. IMPERATIVE PROGRAMMING IS A
PROGRAMMING PARADIGM THAT USES
STATEMENTS THAT CHANGE A
PROGRAM’S STATE.

4. DECLARATIVE PROGRAMMING IS A
PROGRAMMING PARADIGM THAT
EXPRESSES THE LOGIC OF A
COMPUTATION WITHOUT DESCRIBING ITS
CONTROL FLOW.

5. IMPERATIVE VS.
DECLARATIVEHuge paradigm shift. Are you ready?

6. Object-Oriented Programming
▸ The basic idea of OOP is that we use Class & Object to model real-world
things that we want to represent inside our programs.
▸ Classes provide a means of bundling “data” and “behavior” together.
Creating a new class creates a new type of object, allowing new
instances of that type to be made.
Programming or Software Engineering

7. OBJECT
an object represents an individual thing and its
method define how it interacts with other things
A CUSTOM DATA TYPE
CONTAINING BOTH ATTRIBUTES AND
METHODS

8. CLASS
objects are instance of classes
IS A BLUEPRINT FOR THE
OBJECT AND DEFINE WHAT
ATTRIBUTES AND METHODS THE
OBJECT WILL CONTAIN

9. OBJECTS ARE LIKE PEOPLE. THEY ARE LIVING, BREATHING THINGS THAT HAVE KNOWLEDGE INSIDE THEM
ABOUT HOW TO DO THINGS AND HAVE MEMORY INSIDE THEM SO THEY CAN REMEMBER THINGS. AND RATHER
THAN INTERACTING WITH THEM AT A VERY LOW LEVEL, YOU INTERACT WITH THEM AT A VERY HIGH LEVEL OF
ABSTRACTION, LIKE WE’RE DOING RIGHT HERE.
HERE’S AN EXAMPLE: IF I’M YOUR LAUNDRY OBJECT, YOU CAN GIVE ME YOUR DIRTY CLOTHES AND SEND ME A MESSAGE THAT SAYS, “CAN YOU GET MY
CLOTHES LAUNDERED, PLEASE.” I HAPPEN TO KNOW WHERE THE BEST LAUNDRY PLACE IN SAN FRANCISCO IS. AND I SPEAK ENGLISH, AND I HAVE DOLLARS
IN MY POCKETS. SO, I GO OUT AND HAIL A TAXICAB AND TELL THE DRIVER TO TAKE ME TO THIS PLACE IN SAN FRANCISCO. I GO GET YOUR CLOTHES
LAUNDERED, I JUMP BACK IN THE CAB, I GET BACK HERE. I GIVE YOU YOUR CLEAN CLOTHES AND SAY, “HERE ARE YOUR CLEAN CLOTHES.” YOU HAVE NO
IDEA HOW I DID THAT. YOU HAVE NO KNOWLEDGE OF THE LAUNDRY PLACE. MAYBE YOU SPEAK FRENCH, AND YOU CANNOT EVEN HAIL A TAXI. YOU CANNOT
PAY FOR ONE, YOU DO NOT HAVE DOLLARS IN YOUR POCKET. YET I KNEW HOW TO DO ALL OF THAT. AND YOU DIDN’T HAVE TO KNOW ANY OF IT. ALL THAT
COMPLEXITY WAS HIDDEN INSIDE OF ME, AND WE WERE ABLE TO INTERACT AT A VERY HIGH LEVEL OF ABSTRACTION. THAT’S WHAT OBJECTS ARE.THEY
ENCAPSULATE COMPLEXITY, AND THE INTERFACES TO THAT COMPLEXITY ARE HIGH LEVEL.
Do you know who give this
description?

10. Object-Oriented Benefits
▸ Much more easier to maintain.
▸ Code Reuse.
▸ Cleaner Code.
▸ Better Architecture.
▸ Abstraction.
▸ Fewer Faults. Why?
Fault Error Failure
Fault-Tolerance Error MaskingHere we are
Programming or Software Engineering

11. Definition of the Class
▸ A Class is a Template or Blueprint which
is used to instantiate objects. Include:
▸ Data/Attributes/Instance variable
▸ Behavior/Methods
▸ An Object refer to particular instance of a
class where the object contains instance
variables (attributes) and methods defined
in the class.
attributes
Methods
The act of creating object from class is called instantiation

12. O B J E C T ’ S AT T R I B U T E S
REPRESENT THE STATE OF
THE THING WE TRY TO MODEL.
data == attributes == instance variables != class variables

13. Object-Oriented Basic Concepts
Encapsulation Inheritance Polymorphism

14. Encapsulation Concept
▸ Encapsulation is the process of combining attributes and methods that
work on those attributes into a single unit called class.
▸ Attributes are not accessed directly; it is accessed through the methods
present in the class.
▸ Encapsulation ensures that the object’s internal representation (its state
and behavior) are hidden from the rest of the application
attributes
Methods
Information and implementation hiding

15. PYTHON SUPPORT OBJECT-ORIENTED

16. Creating a Class
▸ Classes are defined by using class keyword, followed by ClassName and
a colon.
▸ Class definition must be executed before instantiating an object from it.
class ClassName :
def __init__(self,parameter_1,parameter_2,…):
self.attribute_1 = parameter_1
…
def method_name(self,parameter_1, …):
statement-1
class constructor -
initializing object

17. Example of Creating a Class
▸ Creating a Class for Dog - Any dog
1. class Dog:
2. ‘’’Try to model a real dog ‘’’
3. def __init__(self, name, age):
4. self.name = name
5. self.age = age
6. self.owner = “Not Set Yet ”
7. def sit(self):
8. print(self.name.title() + “ is now sitting “)
9. def roll(self):
10. print(self.name.title() + “ is now rolling “)
11. def set_owner_name(self, name):
12. self.owner = name
Class
Constructor - initialize
attributes
Class Name
method

18. Creating an Object
▸ Creating an Object from a Class:
▸ To access methods and attributes:
▸ To set value outside/inside class definition:
object_name = ClassName(argument_1,argument_2,…)
object_name.attribute_name
object_name.method_name()
arguments will pass
to constructor
object_name.attribute_name = value
self.attributes_name = value
the value can be
int/float/str/bool or
another object
dot operator
connect object with
attributes and methods

19. Example of Creating an Object
▸ The term object and instance of a class are the same thing. Here we
create object my_dog from Dog Class and call method sit() using dot
operator
1. my_dog = Dog(“Diffenbaker”, 6)
2. print(“My dog name is: ” + my_dog.name )
3. my_dog.sit()

20. Modifying Attribute’s Value
▸ Directly:
▸ Through a Method:
1. my_dog = Dog(“Diffenbaker”, 6)
2. my_dog.owner = “Sina”
1. my_dog = Dog(“Diffenbaker”, 6)
2. my_dog.set_owner_name(“Sina”)

21. self must be
always pass to a
method
Class
Constructor
Constructor
arguments
data
attributes

22. no arguments
no
parameters
self is default

24. direct access
access
through a
method

25. WHAT!!! WE CAN ACCESS
T O A N AT T R I B U T E
DIRECTLY?! WHAT HAPPEN
TO ENCAPSULATION?!
Attribute mustn’t be private any more?

26. YOU CAN MAKE A VARIABLE PRIVATE
BY USING 2 UNDERSCORE BEFORE
IT’S NAME AND USING 1 UNDERSCORE
TO MAKE IT PROTECTED
protected is not really protected. It’s just a
hint for a responsible programmer

27. PYTHON DATA PIRACY MODEL IS NOT
WHAT YOU USED TO IN C++/JAVA

28. we can not
directly access a
private attribute
attributes are
private
It’s not a
syntax error but it’s
better not to use () after
Class Name

29. Access
through method

30. TRY TO EXPLAIN WHAT HAPPEN IN THE
NEXT SLIDE CODE?

31. ????

32. CREATING A LIST OF OBJECTS
we can use objects in other data structures

35. USING OBJECTS AS A METHOD ARGUMENT
AND RETURN VALUE

36. list of objectscall
print_students_list()

37. IN PYTHON EVERYTHING
IS AN OBJECTnumbers/str/bool/list/dictionary/…/
function and even class is an object.

38. Object Identity
▸ The id() built-in function is used to find the identity of the location of the
object in memory.
▸ The return value is a unique and constant integer for each object during its
lifetime:
1. my_dog = Dog(“Diffenbaker”, 6)
2. print(id(my_dog) )

39. Identifying Object’s Class
▸ The isinstance() built-in method is check whether an object is an
instance of a given class or not.
isinstance(object_name,ClassName)
True/False

41. Class Attributes vs. Data Attributes
▸ Data Attributes are instance variables that are unique to each object of
a class, and Class attributes are class variables that is shared by all
objects of a class.
Class Attributes are static and they are exist without instantiating an Object

43. Inheritance
▸ Inheritance enables new classes to receive or inherit attributes and
methods of existing classes.
▸ To build a new class, which is already similar to one that already exists, then
instead of creating a new class from scratch you can reference the existing
class and indicate what is different by overriding some of its behavior or by
adding some new functionality.
▸ Inheritance also includes __init__() method.
▸ if you do not define it in a derived class, you will get the one from the base class.
we can also add new attributes.

44. SuperClass
SubClass &
SuperClass
SubClass
More Abstract
Less Abstract
Also Called
Hypernymy
Also Called
Hyponymy
SubClass

45. Inheritance Syntax
class DriveClass(BaseClass):
def __init__(self, drive_class_parameters,base_class_parameters)
super().__init__(base_class_parameters)
self.drive_class_instance_variable = drive_class_parameters

46. SuperClass
to call super
class constructor and
passed name and age
SuperClass

48. WHY OBJECT-ORIENTED AND NOT
CLASS-ORIENTED?

49. “ The Way You Do One Thing
Is the Way You Do
Everything”