"""

12_classes_objects.py

Purpose: classes, instances, attributes, methods, inheritance, __repr__, encapsulation basics.

"""

def h(t): print("\n---", t, "---\n")

h("Basic class and instance")

class Person:

"""Simple person class."""

species = "Homo sapiens" # class attribute

def __init__(self, name, age):

self.name = name # instance attribute

self.age = age

def introduce(self):

return f"My name is {self.name}, age {self.age}"

def __repr__(self):

return f"Person(name={self.name!r}, age={self.age!r})"

p = Person("Khushal", 25)

print(p.introduce())

print("repr:", repr(p))

print("species:", Person.species)

h("Encapsulation and 'private' attributes")

class Counter:

def __init__(self):

self._value = 0 # single underscore: internal by convention

def inc(self):

self._value += 1

def value(self):

return self._value

c = Counter()

c.inc(); c.inc()

print("Counter value:", c.value())

h("Inheritance")

class Student(Person):

def __init__(self, name, age, sid):

super().__init__(name, age)

self.sid = sid

def introduce(self):

base = super().introduce()

return f"{base} (student id: {self.sid})"

s = Student("Aisha", 20, "S123")

print(s.introduce())

h("Polymorphism example")

objs = [p, s]

for o in objs:

print(o.introduce())

h("Mini Exercises")

# 1) Implement a BankAccount class with deposit, withdraw (prevent negative balance), and __repr__.

# 2) Implement classmethod/staticmethod examples and explain use-cases.