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\pard\sa200\sl276\slmult1\f0\fs22\lang9 Classes and Objects Review\par
Python Classes and Objects\par
Class Definition: A class is a blueprint for creating objects. It defines the behavior an object will have through its attributes and methods. Here is a basic example of a class definition in Python:\par
Example Code\par
class Dog:\par
    def __init__(self, name, age):\par
        self.name = name\par
        self.age = age\par
\par
    def bark(self):\par
        print(f'\{self.name.upper()\} says woof woof!')\par
Creating Objects: Objects are instances of a class. They are created by calling the class with the necessary arguments.\par
Example Code\par
dog1 = Dog('Jack', 3)\par
dog2 = Dog('Thatcher', 5)\par
\par
dog1.bark()  # JACK says woof woof!\par
dog2.bark()  # THATCHER says woof woof!\par
Calling Methods on Objects: You can call methods on objects to perform actions or retrieve information.\par
Example Code\par
object_name1.method_name()\par
object_name2.method_name()\par
Difference Between Class and Object: A class is a reusable template, while an object is a specific instance of that class with actual data.\par
Attributes\par
Instance Attributes: Defined in __init__() using self, and unique to each object.\par
Class Attributes: Defined directly inside the class and shared by all instances.\par
Example Code\par
class Dog:\par
    species = 'French Bulldog'  # Class attribute\par
\par
    def __init__(self, name):\par
        self.name = name  # Instance attribute\par
\par
print(Dog.species) # French Bulldog\par
\par
jack = Dog('Jack')\par
print(jack.name)     # Jack\par
print(jack.species)  # French Bulldog\par
Methods\par
Methods: Functions defined inside a class that operate on the object's attributes.\par
Example Code\par
class Car:\par
    def __init__(self, color, model):\par
        self.color = color\par
        self.model = model\par
\par
    def describe(self):\par
        return f'This car is a \{self.color\} \{self.model\}'\par
\par
my_car_1 = Car('red', 'Tesla Model S')\par
print(my_car_1.describe())  # This car is a red Tesla Model S\par
Accessing Methods: Call methods on objects using the dot notation. Here is an example of calling the describe method on two different car objects:\par
Example Code\par
class Car:\par
    def __init__(self, color, model):\par
        self.color = color  \par
        self.model = model  \par
\par
    def describe(self):\par
        return f'This car is a \{self.color\} \{self.model\}'\par
\par
my_car_1 = Car('red', 'Tesla Model S')\par
my_car_2 = Car('green', 'Lamborghini Revuelto')\par
\par
print(my_car_1.describe()) # Calling method using the dot notation\par
\par
print(my_car_2.describe()) # Calling method using the dot notation\par
Dunder (Magic) Methods\par
Definition: Special methods that start and end with a double underscore (e.g., __init__, __len__, __str__, __eq__). Python uses them internally for built-in operations.\par
Example Code\par
class Book:\par
    def __init__(self, title, pages):\par
        self.title = title\par
        self.pages = pages\par
\par
    def __len__(self):\par
        return self.pages\par
\par
    def __str__(self):\par
        return f"'\{self.title\}' has \{self.pages\} pages"\par
\par
    def __eq__(self, other):\par
        return self.pages == other.pages\par
\par
book1 = Book('Built Wealth Like a Boss', 420)\par
print(len(book1))        # 420\par
print(str(book1))        # 'Built Wealth Like a Boss' has 420 pages\par
Calling dunder methods indirectly: You don't need to call dunder methods directly. Instead, Python automatically calls them when certain actions happen. These operations include:\par
\par
arithmetic operations like addition, subtraction, multiplication, division, and others. __add__() is called for addition, __sub__() for subtraction, __mul__() for multiplication, and __truediv__() for division.\par
\par
string operations like concatenation, repetition, formatting, and conversion to text. __add__() is called for concatenation, __mul__() for repetition, __format__() for formatting, __str__() and __repr__() for text conversion, and so on.\par
\par
comparison operations like equality, less-than, greater-than, and others. __eq__() is called for equality checks, __lt__() for less-than, __gt__() for greater-than, and so on.\par
\par
iteration operations like making an object iterable and advancing through items. __iter__() is called to return an iterator and __next__() to fetch the next item.\par
\par
Real World Example: Shopping Cart\par
Cart Class with Dunder Methods: Allows adding, removing, iterating, and checking contents with built-in behavior.\par
Example Code\par
class Cart:\par
    def __init__(self):\par
        self.items = []\par
\par
    def add(self, item):\par
        self.items.append(item)\par
\par
    def remove(self, item):\par
        if item in self.items:\par
            self.items.remove(item)\par
        else:\par
            print(f'\{item\} is not in cart')\par
\par
    def list_items(self):\par
        return self.items\par
\par
    def __len__(self):\par
        return len(self.items)\par
\par
    def __getitem__(self, index):\par
        return self.items[index]\par
\par
    def __contains__(self, item):\par
        return item in self.items\par
\par
    def __iter__(self):\par
        return iter(self.items)\par
\par
cart = Cart()\par
cart.add('Laptop')\par
print(len(cart))        # 1\par
print('Laptop' in cart) # True\par
}