Object Oriented Programming

1. Object Oriented Programming
Lec: 02

2. Create Multiple Objects of Python Class
• # define a class
• class Employee:
• # define an attribute
• employee_id = 0
• # create two objects of the Employee class
• employee1 = Employee()
• employee2 = Employee()
• # access attributes using employee1
• employee1.employee_id = 1001
• print(f"Employee ID: {employee1.employee_id}")
• # access attributes using employee2
• employee2.employee_id= 1002
• print(f"Employee ID: {employee2.employee_id}")
Employee ID: 1001
Employee ID: 1002

3. Behaviors are actions
• Behaviors are actions that can occur on an object.
• The behaviors that can be performed on a specific class of objects are
called methods. At the programming level, methods are like functions in
structured programming, like functions, methods can also accept
parameters and return values.
• Parameters to a method are a list of objects that need to be passed into
the method. These objects are used by the method to perform whatever
behavior or task it is meant to do. Returned values are the results of that
task.

4. Example
• Let's take the example of inventory application.
• One action that can be associated with oranges is the pick action.
pick would place the orange in a basket by updating the basket
attribute of the orange, and by adding the orange to the oranges list
on the Basket. So, pick needs to know what basket it is dealing with.
We do this by giving the pick method a basket parameter. Since our
fruit farmer also sells juice, we can add a squeeze method to Orange.
When squeezed, squeeze might return the amount of juice retrieved,
while also removing the Orange from the basket it was in.

5. Cont.
• Basket can have a sell action. When a basket is sold, our inventory
system might update some data on as-yet unspecified objects for
accounting and profit calculations. Alternatively, our basket of
oranges might go bad before we can sell them, so we add a discard
method. Let's add these methods to our diagram:

6. Hiding details and creating the public interface
• The key purpose of modeling an object in
object-oriented design is to determine
what the public interface of that object will
be.
• The interface is the collection of attributes
and methods that other objects can use to
interact with that object. They do not need,
and are often not allowed, to access the
internal workings of the object. A common
real-world example is the mobile phone.

7. Cont.
• Our interface to the mobile phone is the touch screen. Each action on
the mobile phone either messaging or dialing a number represents a
method that can be called on the mobile phone. When we, as the
calling object, access these methods, we do not know or care if the
mobile phone is getting its signal from an antenna.
• Similarly, we don't care what electronic signals are being sent to
adjust the volume, or whether the sound is destined to speakers or
headphones.

8. Encapsulation
• This process of hiding the implementation, or functional details, of an
object is suitably called information hiding. It is also sometimes referred to
as encapsulation.
• Let’s, take an example of time capsule (A time capsule is a historic cache of
goods or information, usually intended as a deliberate method of
communication with future people)

9. Encapsulation vs Information Hiding
• Encapsulated data is not necessarily hidden. Encapsulation is, literally,
creating a capsule and so think of creating a time capsule. If you put a
bunch of information into a time capsule, lock and bury it, it is both
encapsulated and the information is hidden.
• On the other hand, if the time capsule has not been buried and is
unlocked or made of clear plastic, the items inside it are still
encapsulated, but there is no information hiding

10. Abstraction
• Abstraction is another object-oriented concept related to encapsulation
and information hiding.
• Abstraction means dealing with the level of detail that is most
appropriate to a given task. It is the process of extracting a public
interface from the inner details.
A driver of a car needs to interact with
steering, gas pedal, and brakes. The
workings of the motor, drive train, and
brake subsystem don't matter to the
driver.

11. Cont.
• A mechanic, on the other hand,
works at a different level of
abstraction, tuning the engine
and bleeding the breaks.
Abstraction is the process of encapsulating
information with separate public and private
interfaces

12. Summary
• Objects typically represent nouns in the original problem, while
methods are normally verbs. Attributes can often be picked up as
adjectives, although if the attribute refers to another object that is
part of the current object, it will still likely be a noun. Name classes,
attributes, and methods accordingly.

13. constructor
• Most object-oriented programming languages have the concept of a
constructor, a special method that creates and initializes the object
when it is created.

14. The __init__()
• __init__() is the built-in method.
• All classes have a methods called __init__(), which is always executed
when the class is being initiated.
• Use the __init__() method to assign values to object properties, or other
operations that are necessary to do when the object is being created.
• The __init__() is similar to constructors in C++ and Java. It is run as soon
as an object of a class is instantiated.

15. The self Parameter
• The self parameter is a reference
to the current instance of the
class, and is used to access
variables that belongs to the
class.
• It does not have to be named self
, you can call it whatever you like,
but it has to be the first
parameter of any function in the
class.
class Person:
def __init__(myobject, name, age):
myobject.name = name
myobject.age = age
def myfunc(abc):
print("Hello my name is " + abc.name)
p1 = Person("John", 36)
p1.myfunc()

16. Example 1
• Create a class named Person, use the __init__() function to assign
values for name and age:
class Bike:
def __init__(self, name, gear, speed):
self.name=name
self.gear=gear
self.speed=speed
def gear1(speed):
print(f“ push break{bike1.speed} is dangerous")
bike1=Bike("ali", 12, 70)
bike1.gear1()

17. Example 2
class Dog:
# class attribute
attr1 = "mammal"
# Instance attribute
def __init__(self, name):
self.name = name
def speak(self):
print("My name is
{}".format(self.name))
# Driver code
# Object instantiation
Rodger = Dog("Rodger")
Tommy = Dog("Tommy")
# Accessing class methods
Rodger.speak()
Tommy.speak()

18. Example 3
class Number:
def __init__(self, number):
self.number = number
def even(self, num1):
for c in range(self.number, num1):
print(f"Even numbers are: {c*2}")
a=Number(4)
a.even(14)

19. • Inheritance allows us to define a class that inherits all
the methods and properties from another class.
• Parent class is the class being inherited from, also
called base class.
• Child class is the class that inherits from another
class, also called derived class.

20. For practical purpose
• Anaconda: https://anaconda.org/
• Jupyter notebook