CMPE-103-Module-6-Abstraction-and-Encapsulation.pdf

CMPE 103 Module 6 ABSTRACTION AND ENCAPSULATION Campus class Employee: Encapsulation allows us to restrict accessing # constructor variables and methods directly and prevent def __init__(self, name, salary,...

CMPE 103 Module 6 ABSTRACTION AND ENCAPSULATION Campus class Employee: Encapsulation allows us to restrict accessing # constructor variables and methods directly and prevent def __init__(self, name, salary, project): accidental data modification by creating private # data members data members and methods within a class. self.name = name self.salary = salary self.project = project Encapsulation is a way can restrict access to methods and variables from outside of class. # method Whenever we are working with the class and # to display employee's details dealing with sensitive data, providing access to all def show(self): variables used within the class is not a good choice. # accessing public data member print("Name: ", self.name, 'Salary:', self.salary) # method def work(self): print(self.name, 'is working on', self.project) # creating object of a class emp = Employee('Jessa', 8000, 'NLP') # calling public method of the class emp.show() emp.work() Access modifiers limit access to the variables and methods of a class. Python provides three types of access modifiers private, public, and protected. Public Member: Accessible anywhere from outside class. Private Member: Accessible within the class Protected Member: Accessible within the class and its sub-classes Public Member Public data members are accessible within and outside of a class. All member variables of the class are by defaultclass public.Employee: # constructor def __init__(self, name, salary): # public data members self.name = name self.salary = salary # public instance methods def show(self): # accessing public data member print("Name: ", self.name, 'Salary:', self.salary) # creating object of a class emp = Employee('Jessa', 10000) # accessing public data members print("Name: ", emp.name, 'Salary:', emp.salary) # calling public method of the class emp.show() Private Member We can protect variables in the class by marking them private. To define a private variable, add two underscores as a prefix at the start of a variable name. Private members are accessible only within the class, and we can’t access them directly from the class objects. class Employee: # constructor def __init__(self, name, salary): # public data member self.name = name Output: # private member AttributeError: 'Employee' object has no attribute '__salary' self.__salary = salary # creating object of a class emp = Employee('Jessa', 10000) # accessing private data members print('Salary:', emp.__salary) We can access private members from outside of a class using the following two approaches Create public method to access private members Use Publicname methodmangling to access private members Access Private member outside of a class using an instance method class Employee: # constructor def __init__(self, name, salary): # public data member self.name = name # private member self.__salary = salary # public instance methods def show(self): # private members are accessible from a class print("Name: ", self.name, 'Salary:', self.__salary) # creating object of a class emp = Employee('Jessa', 10000) # calling public method of the class emp.show() Name Mangling to access private members We can directly access private and protected variables from outside of a class through name mangling. The name mangling is created on an identifier by adding two leading underscores and one trailing underscore, like this _classname__dataMember, where classname is the current class, and data member is the private variable name. class Employee: # constructor def __init__(self, name, salary): # public data member self.name = name # private member self.__salary = salary # creating object of a class emp = Employee('Jessa', 10000) print('Name:', emp.name) # direct access to private member using name mangling print('Salary:', emp._Employee__salary) Protected Member Protected members are accessible within the class and also available to its sub-classes. To define a protected member, prefix the member's name with a single underscore _. Protected data members are used when you implement inheritance and want to allow data members access to only child classes. # base class class Company: def __init__(self): # Protected member self._project = "NLP" # child class class Employee(Company): def __init__(self, name): self.name = name Company.__init__(self) def show(self): print("Employee name :", self.name) # Accessing protected member in child class print("Working on project :", self._project) c = Employee("Jessa") c.show() # Direct access protected data member print('Project:', c._project) Getters and Setters in Python To implement proper encapsulation in Python, we need to use setters and getters. The primary purpose of using getters and setters in object- oriented programs is to ensure data encapsulation. Use the getter method to access data members and the setter methods to modify the data members. In Python, private variables are not hidden fields like in other programming languages. The getters and setters methods are often used when: When we want to avoid direct access to private variables To add validation logic for setting a value class Student: def __init__(self, name, age): # private member Output: self.name = name Name: Jessa 14 self.__age = age Name: Jessa 16 # getter method def get_age(self): return self.__age # setter method def set_age(self, age): self.__age = age stud = Student('Jessa', 14) # retrieving age using getter print('Name:', stud.name, stud.get_age()) # changing age using setter stud.set_age(16) # retrieving age using getter print('Name:', stud.name, stud.get_age()) Information Hiding and conditional logic for setting an object attributes class Student: def __init__(self, name, stud_no, age): # private member self.name = name Output: # private members to restrict access Student Details: Jessa 10 # avoid direct data modification self.__stud_no = stud_no Invalid stud no. Please set correct student number self.__age = age Student Details: Jessa 25 def show(self): print('Student Details:', self.name, self.__stud_no) # getter methods def get_stud_no(self): return self.__stud_no # setter method to modify data member # condition to allow data modification with rules def set_stud_no(self, number): if number > 50: print('Invalid stud no. Please set correct student number') else: self.__stud_no = number jessa = Student('Jessa', 10, 15) # before Modify jessa.show() # changing student number using setter jessa.set_stud_no(120) jessa.set_stud_no(25) jessa.show() Advantages of Encapsulation Security: The main advantage of using encapsulation is the security of the data. Encapsulation protects an object from unauthorized access. It allows private and protected access levels to prevent accidental data modification. Data Hiding: The user would not be knowing what is going on behind the scene. They would only be knowing that to modify a data member, call the setter method. To read a data member, call the getter method. What these setter and getter methods are doing is hidden from them. Simplicity: It simplifies the maintenance of the application by keeping classes separated and preventing them from tightly coupling with each other. Aesthetics: Bundling data and methods within a class makes code more readable and maintainable Try and run this programming problem (The Fan class). Design a class named Fan to represent a fan. The class contains: Three constants named SLOW, MEDIUM, and FAST with the values 1, 2, and 3 to denote the fan speed. A private int data field named speed that specifies the speed of the fan. A private bool data field named on that specifies whether the fan is on (the default is False). A private float data field named radius that specifies the radius of the fan. A private string data field named color that specifies the color of the fan. The accessor(getters) and mutator(setters) methods for all four data fields. A constructor that creates a fan with the specified speed (default SLOW), radius (default 5), color (default blue), and on (default False). Write a test program named TestFan that creates two Fan objects. For the first object, assign the maximum speed, radius 10, color yellow, and turn it on. Assign medium speed, radius 5, color blue, and turn it off for the second object. Display each object’s speed, radius, color, Programming Exercise: A. Car Class Write a class named Car that has the following data attributes: _ _year_model (for the car’s year model) _ _make (for the make of the car) _ _speed (for the car’s current speed) The Car class should have an _ _init_ _ method that accepts the car’s year model and make as arguments. These values should be assigned to the object’s _ _year_model and _ _make data attributes. It should also assign 0 to the _ _speed data attribute. The class should also have the following methods: accelerate() The accelerate method should add 5 to the speed data attribute each time it is called. brake() The brake method should subtract 5 from the speed data attribute each time it is called. get_speed() The get_speed method should return the current speed. Next, design a program that creates a Car object then calls the accelerate method five times. After each call to the accelerate method, get the current speed of the car and display it. Then call the brake method five times. After each call to the brake method, get the current speed of the car and display it. B. Pet Class Write a class named Pet, which should have the following data attributes: _ _name (for the name of a pet) _ _animal_type (for the type of animal that a pet is. Example values are ‘Dog’, ‘Cat’, and ‘Bird’) _ _age (for the pet’s age) The Pet class should have an _ _init_ _ method that creates these attributes. It should also have the following methods: set_name() This method assigns a value to the _ _name field. set_animal_type() This method assigns a value to the _ _animal_type field. set_age() This method assigns a value to the _ _age field. get_name() This method returns the value of the _ _ name field. get_animal_type() This method returns the value of the _ _animal_type field. get_age() This method returns the value of the _ _age field. Once you have written the class, write a program that creates an object of the class and prompts the user to enter the name, type, and age of his or her pet. This data should be stored as the object’s attributes. Use the object’s accessor methods to retrieve the pet’s name, type, and age and display this data on the screen.