oop.py

# ===========================================
# OOP PLAYGROUND PROJECT
# Learn about: classes, objects, attributes, methods,
# constructors, encapsulation, inheritance, polymorphism

# Class definition: Blueprint for creating objects
# Objects: Instances of a class
# Attributes: Variables inside a class
# Methods: Functions inside a class
# Constructor (__init__): Initializes object attributes
# Encapsulation: Private attributes with getters/setters
# Inheritance: Child class extending a parent
# Polymorphism: Methods behaving differently in subclasses

# ===========================================

# ---------------------------
# CLASS & OBJECTS
# ---------------------------


class Student:
    """A class to represent a student."""

    # Constructor: initializes an object with attributes
    def __init__(self, name, age, grade):
        self.name = name          # public attribute
        self.age = age
        self.__grade = grade      # private attribute (encapsulation with __)

    # Method: a function that belongs to the class
    def introduce(self):
        print(f"Hi, my name is {self.name} and I am {self.age} years old.")

    # Getter method to access private attribute
    def get_grade(self):
        return self.__grade

    # Setter method to safely change private attribute
    def set_grade(self, grade):
        if 0 <= grade <= 100:  # simple validation
            self.__grade = grade
        else:
            print("Invalid grade. Must be between 0 and 100.")

# ---------------------------
# INHERITANCE
# ---------------------------

class GraduateStudent(Student):
    """A class that inherits from Student"""

    def __init__(self, name, age, grade, thesis_title):
        # Call parent constructor using super()
        super().__init__(name, age, grade)
        self.thesis_title = thesis_title

    # Polymorphism: override introduce() method
    def introduce(self):
        print(f"I am {self.name}, a graduate student.")
        print(f"My thesis is titled: '{self.thesis_title}'")

# ---------------------------
# OBJECT CREATION
# ---------------------------

# Create an object (instance) of Student
student1 = Student("Alice", 20, 88)
student1.introduce()
print("Alice's grade:", student1.get_grade())

# Try changing grade using setter
student1.set_grade(95)
print("Alice's new grade:", student1.get_grade())

# Create another object
student2 = Student("Bob", 19, 76)
student2.introduce()

# Create a GraduateStudent object
grad_student = GraduateStudent("Charlie", 25, 90, "AI in Healthcare")
grad_student.introduce()
print("Charlie's grade:", grad_student.get_grade())

# ---------------------------
# USING A LIST OF OBJECTS
# ---------------------------

# Store objects in a list and loop through them
print("\n--- List of Students ---")
students = [student1, student2, grad_student]

for s in students:
    s.introduce()   # polymorphism in action (different introduce() behavior)


# Concepts Illustrated:
# 
# Class: Defines a blueprint using 'class Student'.
# 
# Object: Creates an instance with 'student1 = Student("Alice", 20, 88)'.
# 
# Attributes: Includes 'self.name', 'self.age', and 'self.__grade'.
# 
# Methods: Functions like 'introduce()', 'get_grade()', and 'set_grade()'.
# 
# Constructor: '__init__' method initializes attributes.
# 
# Encapsulation: '__grade' is private, accessed via getter & setter.
# 
# Inheritance: 'GraduateStudent' inherits from 'Student'.
# 
# Polymorphism: 'introduce()' method behaves differently in 'Student' and 'GraduateStudent'.
# 
# List of objects: Stores multiple students and iterates over them.