Abstraction: -
§ Hiding
the internal implementation and highlighting the set of services that process
is called abstraction.
§ Another
way, it shows only important things to the user and hides the internal details
for example sending SMS, you just type the text and send the message. You don’t
know the internal processing about the message delivery.
§ Abstraction
lets you focus on what the object does instead of how it does it.
Ex:-
a. Bank
ATM Screens (Hiding thee internal implementation and highlighting set of
services like withdraw, money transfer, mobile registration).
b. Mobile
phones (The mobile persons are hiding the internal circuit implementation and
highlighting touch screen).
c. Syllabus
copy (the institutions persons just highlighting the set of contents that
persons provided the persons are not highlighting the whole content).
Abstract Classes in Python
§
An abstract class can be considered
as a blueprint for other classes, allows you to create a set of methods that
must be created within any child classes built from your abstract class.
§
A class which contains one or
abstract methods is called an abstract class. An abstract method is a method
that has declaration but not has any implementation.
§
Abstract classes are not able to
instantiate, and it needs subclasses to provide implementations for those
abstract methods which are defined in abstract classes. While we are designing
large functional units, we use an abstract class.
§
When we want to provide a common
implemented functionality for all implementations of a component, we use an abstract
class. Abstract classes allow partially to implement classes when it completely
implements all methods in a class, then it is called interface.
Why use Abstract Base
Classes :
§
Abstract classes allow you to
provide default functionality for the subclasses. Compared to interfaces
abstract classes can have an implementation.
By
defining an abstract base class, you can define a common Application Program
Interface (API) for a set of subclasses. This capability is especially useful
in situations where a third-party is going to provide implementations, such as
with plugins in an application, but can also help you when working on a large
team or with a large code-base where keeping all classes in your head at the
same time is difficult or not possible.
v Abstract classes are classes
that contain one or more abstract methods. An abstract method is a method that
is declared, but contains no implementation. Abstract classes may not be
instantiated, and require subclasses to provide implementations for the abstract
methods. Subclasses of an abstract class in Python are not required to
implement abstract methods of the parent class.
Abstract Method in Python
§ Abstract method is a method
whose definition is implemented in the sub classes as per the requirements of
the objects.
§ Abstract methods consist of
only methods declarations, without any method body.
How to Abstract Method in Python
§ The method
with-out any implementation is known as undefine method.
§ An abstract method
is a method that is declared without an implementation
§ The abstract method
decorator registers the method as undefined method
@abstractmethod
@abstractmethod
def method-name(self):
pass
How
Abstract Base classes work :
class C1:
def m1(self):
pass
class C2(C1):
pass
#Create an object of
C1
obj1=C1()
#Create an object of
C2
obj2=C2()
v If we start this program, we see that this is not an
abstract class, because we can instantiate an instance from
§
we are not required to implement m1
in the class definition of C2
v
In python by default, it is not able
to provide abstract classes, but python comes up with a module which provides
the base for defining Abstract Base classes (ABC) and that module name is ABC. ABC works
by marking methods of the base class as abstract and then registering concrete
classes as implementations of the abstract base. A method becomes an abstract
by decorated it with a keyword @abstractmethod.
For Example –
The following Python code uses the
abc module and defines an abstract base class:
from abc import ABC,
abstractmethod
class C1(ABC):
# the abstractmethod
decorator registers this method as undefined
@abstractmethod
def m1(self):
pass
#Create an object of
C1
obj1=C1()
obj1=C1()
TypeError: Can't
instantiate abstract class C1 with abstract methods m1
§ Now we will define
a subclass using the C1 defined abstract class. You will notice that we haven't
implemented the m1() method, even though
we are required to implement it, because this method is decorated as an
abstract method with the decorator "abstractmethod". We get an
exception :
class C2(C1):
pass
#Create an object of C2
obj2=C2()
obj2=C2()
TypeError: Can't instantiate abstract class C2 with abstract methods
m1
§
If
the child class haven't implemented the parent class abstract method then child
class also becomes abstract class. Then child class can’t be instantiated.
A class that is derived from an
abstract class cannot be instantiated unless all of its abstract methods are
overridden.
Ø Ex: -the abstract class
contains abstract methods for that abstract methods
provide the implementation
in child classes.
from abc import ABC,
abstractmethod
class Test1(ABC):
def m1(self):
pass
def m2(self):
pass
def m3(self):
pass
class Test2(Test1):
def m1(self):
print('m1-method
defined by Test2 Class')
def m2(self):
print('m2-method
defined by Test2 Class')
def m3(self):
print('m3-method
defined by Test3 Class')
#Creating Child Class
Object
t2=Test2()
t2.m1()
t2.m2()
t2.m3()
output:
m1-method defined by Test2
Class
m2-method defined by Test2
Class
m3-method defined by Test3
Class
Ø Ex: - if the child class is
unable to provide the implementation for parent class
abstract methods at that situation,
we can declare that class is an abstract then take one more child class in that
class provide the implementation for remaining methods.
§ Whenever we inherit ‘n’ number of abstract methods
from abstract base class o derived class, if the derived class defines all ‘n’
number of abstract methods then the derived class is concrete class. If the
derived class is not defining at least one abstract method out of ‘n’ abstract
methods then the derived class is known as abstract derived class and to make
that class abstract, we use a keyword called abstract
§ An abstract base class is one which contains physical
representation of abstract methods. An abstract derived class is one which
contains logical declaration of abstract methods which are inherited from
abstract base class.
from abc import ABC,
abstractmethod
class Test1(ABC):
def m1(self):
pass
def m2(self):
pass
def m3(self):
pass
class Test2(Test1):
def m1(self):
print('m1-method
defined by Test2 Class')
def m2(self):
print('m2-method
defined by Test2 Class')
class Test3(Test2):
def m3(self):
print('m3-method defined by
Test3 Class')
#Creating Child Class
Object
t=Test3()
t.m1()
t.m2()
t.m3()
output:
m1-method defined by
Test2 Class
m2-method defined by
Test2 Class
m3-method defined by
Test3 Class
v Demo
Program with Polygon Abstract Class
§
Polygon class that will hold
common properties and behaviors for its inheriting classes.
§
Here we have the abstract class
Polygon. we have defined noofsides behaviors which are present in all
Polygons.
§ Polygon can be abstraction for
a Triangle,Pentagon,Hexagon,Quadrilateral etc. It acts as a super-categorial
noun.
§
As an abstract concept it can
hold all the common properties and behaviors present in different figure.
Program
from abc import ABC,
abstractmethod
class Polygon(ABC):
# the abstractmethod
decorator registers this method as undefined
@abstractmethod
def noofsides(self):
pass
class Triangle(Polygon):
# overriding abstract method
def noofsides(self):
print("Triangle
have 3 sides")
class Pentagon(Polygon):
# overriding abstract method
def noofsides(self):
print("Pentagon
have 5 sides")
class Hexagon(Polygon):
# overriding abstract method
def noofsides(self):
print("Hexagon
have 6 sides")
class Quadrilateral(Polygon):
# overriding abstract method
def noofsides(self):
print("Quadrilateral
have 4 sides")
# Driver code
T = Triangle()
T.noofsides()
Q = Quadrilateral()
Q.noofsides()
P = Pentagon()
P.noofsides()
H = Hexagon()
H.noofsides()
output:
Triangle have 3 sides
Quadrilateral have 4 sides
Pentagon have 5 sides
Hexagon have 6 sides
Demo Program with Shape Abstract Class
§
Here we have the abstract class
Shape. We have defined behaviors area () and perimeter () behaviors which are
present in all Shape.
§
Now we have three concreate
classes Rectangle,Sqaure,Circle
inheriting from the Shape abstract class.
§
Shape can be abstraction for a
Rectangle,Sqaure,Circle etc. It acts as
a super-categorial noun.
from abc import ABC,
abstractmethod
class Shape(ABC):
# the abstractmethod
decorator registers this method as undefined
@abstractmethod
def area(self):
pass
@abstractmethod
def perimeter(self):
pass
class Rectangle(Shape):
def __init__(self,l,b):
self.l=l
self.b=b
def area(self):
return (self.l*self.b)
def perimeter(self):
return (2*(self.l+self.b))
class Square(Shape):
def __init__(self,side):
self.side=side
def area(self):
return (self.side*self.side)
def perimeter(self):
return (4*(self.side))
class Circle(Shape):
def __init__(self,radius):
self.radius=radius
def area(self):
return 3.14*(self.radius**2)
def perimeter(self):
return (2*3.14*self.radius)
#Creating Rectangle
Class Object
r1=Rectangle(10,20)
print('Area
of Rectangle=',r1.area())
print('Perimeter
of Rectangle=',r1.perimeter())
#Creating Square Class
Object
s1=Square(10)
print('Area
of Square=',s1.area())
print('Perimeter
of Square=',s1.perimeter())
#Creating Circle Class
Object
c1=Circle(1.2)
print('Area
of Circle=',c1.area())
print('Perimeter of Circle=',c1.perimeter())
output:
Area of Rectangle= 200
Perimeter of Rectangle= 60
Area of Square= 100
Perimeter of Square= 40
Area of Circle= 4.5216
Perimeter of Circle= 7.536
Concrete
Methods in Abstract Base Classes:
§
Concrete classes contain only
concrete (normal)methods whereas abstract classes may contain both concrete
methods and abstract methods.
Demo Program with Account Abstract Class
§
Account class that will hold
common properties and behaviors for its inheriting classes.
§
Here we have the abstract class
Account. We have defined properties & behaviors which are present in all
Account.
Properties
accno
accholderName
balance
Behaviors
deposit(amount)
withdraw(amount)
balanceEnquiry()
§
Now we have two concreate
classes inheriting from the Account abstract class. We have added some more
behaviors specific to the entities.
§
Account can be abstraction for
a CurrentAccount and SavingAccount etc. It acts as a super-categorial noun.
from abc import ABC,
abstractmethod
class Account(ABC):
def __init__(self,accno,accholderName):
self.accno=accno
self.accholderName=accholderName
self.balance=0
# the abstractmethod
decorator registers this method as undefined
@abstractmethod
def deposit(self,amount):
pass
@abstractmethod
def withdraw(self,amount):
pass
def balanceEnquiry(self):
return self.balance
class CurrentAccount(Account):
def __init__(self,accno,accholderName):
super().__init__(accno,accholderName)
def deposit(self,amount):
print(amount,'Rs.
Credit in your Current Account')
self.balance=self.balance+amount
def withdraw(self,amount):
print(amount,'Rs.
debit from your Current Account')
self.balance=self.balance-amount
def processToCheck(self,chequeNo):
print('Transaction
Process through Cheque')
class SavingAccount(Account):
def __init__(self,accno,accholderName):
super().__init__(accno,accholderName)
self.interest=0
def deposit(self,amount):
print(amount,'Rs.
Credit in your Saving Account')
self.balance=self.balance+amount
def withdraw(self,amount):
print(amount,'Rs.
debit from your Saving Account')
self.balance=self.balance-amount
def monthlyInterest(self):
self.interest=self.balance*0.05
#Driver Code
ca=CurrentAccount(12345,'John')
ca.deposit(10000)
print('Current
Balance= ',ca.balanceEnquiry())
ca.withdraw(500)
print('Current
Balance= ',ca.balanceEnquiry())
#Creating SavingAccount
Object
sa=SavingAccount(784578,'Harry')
sa.deposit(5000)
print('Current
Balance= ',sa.balanceEnquiry())
sa.withdraw(500)
print('Current
Balance= ',sa.balanceEnquiry())
output:
10000 Rs. Credit in
your Current Account
Current Balance= 10000
500 Rs. debit from your
Current Account
Current Balance= 9500
5000 Rs. Credit in your
Saving Account
Current Balance= 5000
500 Rs. debit from your
Saving Account
Current Balance= 4500
Demo Program with Plan Abstract Class
§
Plan class that will hold
common properties and behaviors for its inheriting classes.
§ Here we have the abstract class
Plan.We have defined properties rate & behaviors setRate(),calculateBill(units)
which are present in all Plan
§
Now we have Three concreate classes
inheriting from the Plan abstract class.
§
Plan can be abstraction for a
DomesticPlan and CommercialPlan,InstitutionalPlan etc. It acts as a
super-categorial noun.
Calculate Electricity Bill : A
Real World Example of Factory Method
Step 1: Create a
Plan abstract class.
from abc import ABC,
abstractmethod
#Create a Plan
abstract class.
class Plan:
def __init__(self):
self.rate=0.0
#the abstractmethod decorator
registers this method as undefined
@abstractmethod
def setRate(self):
pass
def calculateBill(self,
units):
print(units*self.rate)
Step 2: Create
the concrete classes that inherit Plan
abstract class.
class DomesticPlan(Plan):
def setRate(self):
self.rate=3.6
class CommercialPlan(Plan):
def setRate(self):
self.rate=4.2
class InstitutionalPlan
(Plan):
def setRate(self):
self.rate=5.3
Step 3: Create a
GetPlanFactory to generate object of concrete classes based on
given information.
class GetPlanFactory:
#use getPlan method to get
object of type Plan
def getPlan(self,planType):
if
planType==None:
return None
elif
planType=='DOMESTICPLAN':
return
DomesticPlan()
elif
planType=='COMMERCIALPLAN':
return
CommercialPlan()
elif
planType=='INSTITUTIONALPLAN':
return InstitutionalPlan()
else:
return 'Plz
Provide Valid Plan Only!.'
Step 4: Generate
Bill by using the GetPlanFactory to get the object of concrete classes by
passing an information such as type of plan DOMESTICPLAN or COMMERCIALPLAN or
INSTITUTIONALPLAN
#Driver Code
planFactory = GetPlanFactory();
print("Enter
the name of plan for which the bill will be generated: ");
print('1.DOMESTICPLAN\n2.COMMERCIALPLAN\n3.INSTITUTIONALPLAN')
planName=input('enter
plan Type')
planName=planName.upper()
units=int(input('Enter
the number of units for bill will be calculated:'))
plan=
planFactory.getPlan(planName);
print("Bill
amount for ",planName," of ",units,"
units is: ");
plan.setRate();
plan.calculateBill(units);
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