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<!DOCTYPE html>
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<head>
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  <meta name="description"
        content="Chapter 11 of Python Zero to Hero: dive into Object-Oriented Programming—classes, objects, methods, inheritance, and special methods."/>
  <meta name="keywords"
        content="Python, OOP, class, object, method, inheritance, polymorphism, __init__, dunder methods, encapsulation, property"/>
  <meta name="author" content="Luca Bocaletto"/>
  <title>Chapter 11 – Object-Oriented Programming | Python Zero to Hero</title>

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    <header class="my-4">
      <h1 class="display-6">Chapter 11: Object-Oriented Programming</h1>
      <p class="text-muted">
        Learn how to define classes, create objects, manage inheritance and use Python’s special methods.
      </p>
      <a href="src/chapter11.py" download class="btn btn-outline-primary btn-sm btn-py">
        Download <code>chapter11.py</code>
      </a>
      <hr>
    </header>

    <!-- Objectives -->
    <section id="objectives" class="mb-5">
      <h2>Objectives</h2>
      <ul>
        <li>Define classes and instantiate objects.</li>
        <li>Use instance methods and attributes, and the <code>__init__</code> initializer.</li>
        <li>Work with class variables, classmethods and staticmethods.</li>
        <li>Implement inheritance, method overriding and polymorphism.</li>
        <li>Employ special (“dunder”) methods to customize behavior.</li>
        <li>Encapsulate data with private attributes and <code>@property</code>.</li>
      </ul>
    </section>

    <!-- 1. Classes & Instances -->
    <section id="classes" class="mb-5">
      <h2>1. Classes &amp; Instances</h2>
      <p>Define a class and its <code>__init__</code> constructor:</p>
      <pre><code class="python">class Person:
    def __init__(self, name, age):
        self.name = name      # instance attribute
        self.age = age

# Instantiate
alice = Person("Alice", 30)
print(alice.name, alice.age)  # Alice 30
</code></pre>
    </section>

    <!-- 2. Methods & Attributes -->
    <section id="methods" class="mb-5">
      <h2>2. Instance &amp; Class Members</h2>
      <p>Instance methods operate on <code>self</code>; class variables shared across instances:</p>
      <pre><code class="python">class Counter:
    total = 0              # class variable

    def __init__(self):
        Counter.total += 1
        self.id = Counter.total

    def greet(self):
        return f"Instance {self.id} says hello"

# Usage
c1 = Counter(); c2 = Counter()
print(c1.greet(), c2.greet())
print("Total instances:", Counter.total)
</code></pre>
    </section>

    <!-- 3. Inheritance & Polymorphism -->
    <section id="inheritance" class="mb-5">
      <h2>3. Inheritance &amp; Polymorphism</h2>
      <p>Subclass to extend or override behavior:</p>
      <pre><code class="python">class Animal:
    def speak(self):
        raise NotImplementedError

class Dog(Animal):
    def speak(self):
        return "Woof!"

class Cat(Animal):
    def speak(self):
        return "Meow!"

for pet in (Dog(), Cat()):
    print(pet.speak())    # Woof! Meow!
</code></pre>
    </section>

    <!-- 4. Special Methods -->
    <section id="dunder" class="mb-5">
      <h2>4. Special Methods</h2>
      <p>Implement <code>__str__</code>, <code>__repr__</code>, <code>__eq__</code> for rich behavior:</p>
      <pre><code class="python">class Point:
    def __init__(self, x, y):
        self.x, self.y = x, y

    def __repr__(self):
        return f"Point({self.x},{self.y})"

    def __eq__(self, other):
        return isinstance(other, Point) and (self.x, self.y)==(other.x, other.y)

p1, p2 = Point(1,2), Point(1,2)
print(p1, p2, p1==p2)   # Point(1,2) Point(1,2) True
</code></pre>
    </section>

    <!-- 5. Encapsulation & Properties -->
    <section id="encapsulation" class="mb-5">
      <h2>5. Encapsulation &amp; @property</h2>
      <p>Use name mangling for “private” attributes and <code>@property</code> for getters/setters:</p>
      <pre><code class="python">class Account:
    def __init__(self, bal):
        self.__balance = bal

    @property
    def balance(self):
        return self.__balance

    @balance.setter
    def balance(self, val):
        if val<0:
            raise ValueError("Negative balance")
        self.__balance = val

acct = Account(100)
print(acct.balance)      # 100
acct.balance = 150
# acct.balance = -50    # ValueError
</code></pre>
    </section>

    <!-- Exercises -->
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      <h2>Exercises</h2>
      <ol>
        <li>Define a <code>Rectangle</code> class with <code>width</code>, <code>height</code> and a method <code>area()</code>.</li>
        <li>Implement a <code>Vehicle</code> base class and subclasses <code>Car</code>, <code>Bike</code> overriding a <code>move()</code> method.</li>
        <li>Create a <code>Vector</code> class supporting +, -, * via <code>__add__</code>, <code>__sub__</code>, <code>__mul__</code>.</li>
        <li>Use <code>@property</code> to create a read-only <code>full_name</code> from <code>first_name</code> and <code>last_name</code>.</li>
      </ol>
    </section>

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