Chapter 7: Understand the Object-Oriented Approach in Python
Chapter 7: Class, Object, and Members in Python
Python is an object-oriented programming (OOP) language, which means it allows developers to design and build programs based on objects and their interactions. This chapter dives into the core OOP principles and explores how Python implements them.
7.1 Class, Object, and Members in Python
- Class:
A class is a blueprint for creating objects. It defines a set of attributes and methods that characterize any object of the class.
Syntax:
class ClassName:
# Attributes and methods
- Object:
An object is an instance of a class. When a class is defined, no memory is allocated until an object is created.
Syntax:
obj = ClassName()
- Class Members:
- Attributes: Variables inside a class that represent data about the object.
- Methods: Functions inside a class that define the behaviors of the object.
- Access Modifiers: Determine the visibility of class members (
public,_protected,__private).
Example:
class Person:
def __init__(self, name, age):
self.name = name
self.age = age
def greet(self):
return f"Hello, my name is {self.name}."
# Creating an object
person1 = Person("Alice", 25)
print(person1.greet()) # Output: Hello, my name is Alice.
7.2 Inheritance
Inheritance allows a class (child) to inherit attributes and methods from another class (parent). It promotes code reuse and establishes a hierarchical relationship.
- Syntax:
class Parent:
# Parent class code
class Child(Parent):
# Child class code
Example:
class Animal:
def sound(self):
return "This is a generic sound."
class Dog(Animal):
def sound(self):
return "Bark"
dog = Dog()
print(dog.sound()) # Output: Bark
7.3 Polymorphism
Polymorphism means "many forms." It allows methods in different classes to share the same name, offering flexibility.
Example:
class Bird:
def fly(self):
return "Some birds can fly."
class Penguin(Bird):
def fly(self):
return "Penguins cannot fly."
def flying_test(bird):
print(bird.fly())
sparrow = Bird()
penguin = Penguin()
flying_test(sparrow) # Output: Some birds can fly.
flying_test(penguin) # Output: Penguins cannot fly.
7.4 Encapsulation
Encapsulation restricts direct access to some of an object's components, providing controlled access via methods. This is achieved using access modifiers.
- Public Members: Accessible everywhere.
- Protected Members: Prefix with
_. Accessible in the class and its subclasses. - Private Members: Prefix with
__. Accessible only within the class.
Example:
class Car:
def __init__(self, brand, speed):
self.brand = brand # Public
self._speed = speed # Protected
self.__engine_number = 12345 # Private
def get_engine_number(self):
return self.__engine_number
car = Car("Toyota", 120)
print(car.brand) # Public access
print(car._speed) # Accessible but discouraged
print(car.get_engine_number()) # Controlled access to private
7.5 Data Hiding & Object Printing
- Data Hiding: Encapsulation aids in hiding implementation details. Only necessary information is exposed through methods.
- Object Printing: By overriding the
__str__or__repr__methods, we can customize object representation.
Example:
class Book:
def __init__(self, title, author):
self.title = title
self.author = author
def __str__(self):
return f"'{self.title}' by {self.author}"
book = Book("1984", "George Orwell")
print(book) # Output: '1984' by George Orwell
7.6 Constructors
A constructor is a special method used to initialize objects. In Python, the __init__ method acts as the constructor.
Example:
class Student:
def __init__(self, name, grade):
self.name = name
self.grade = grade
student = Student("John", "A")
print(student.name) # Output: John
7.7 Destructors in Python
A destructor is used to perform cleanup operations when an object is deleted. Python provides the __del__ method as a destructor.
Example:
class File:
def __init__(self, name):
self.name = name
def __del__(self):
print(f"Closing file: {self.name}")
file = File("example.txt")
del file # Output: Closing file: example.txt
7.8 Garbage Collection in Python
Python has an automatic garbage collection system that reclaims unused memory. The gc module provides tools for manual garbage collection.
Example:
import gc
# Enable garbage collection
gc.enable()
# Check if garbage collection is enabled
print(gc.isenabled()) # Output: True
7.9 Conclusions
Object-oriented programming in Python provides a structured and modular way to design software. Key principles such as inheritance, polymorphism, encapsulation, and data hiding allow for code reuse, flexibility, and robustness. Python’s support for constructors, destructors, and automatic garbage collection simplifies memory management, making it a powerful language for developing scalable and maintainable applications.
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