day8_cheatsheet.md

🐍 Python Day 8 Cheat Sheet

Introduction to Object-Oriented Programming (OOP)

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📝 Table of Contents

1. Core Definitions
2. Class Syntax
3. Creating and Using Objects
4. Quick Reference
5. Common Mistakes to Avoid

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🧠 Core Definitions

• Class: A blueprint for creating objects. It defines a set of attributes and methods that the created objects will have.
• Object (or Instance): A specific item created from a class. If Dog is the class, a specific dog named Fido is an object.
• Attribute: A variable that belongs to an object. It represents a piece of data about the object (e.g., dog.name, dog.age).
• Method: A function that belongs to an object. It represents an action the object can perform (e.g., dog.bark()).
• __init__(): A special method called the "constructor". It runs automatically when a new object is created and is used to set up the object's initial attributes.
• self: A special parameter that must be the first parameter of every method in a class. It refers to the object instance itself, giving the method access to the object's attributes and other methods.

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🏛️ Class Syntax

Defining a Simple Class

The basic structure of a class with an __init__ method and another method.

# Class names are typically written in PascalCase (first letter of each word capitalized).
class Dog:
    # The constructor method to initialize the object's attributes.
    def __init__(self, name, age):
        # 'self' refers to the instance being created.
        # These are the attributes.
        self.name = name
        self.age = age

    # This is a method. It's a function that belongs to the class.
    # It must have 'self' as its first parameter.
    def bark(self):
        print(f"{self.name} says: Woof!")

Attributes with Default Values

You can set a default value for an attribute directly in the __init__ method.

class Car:
    def __init__(self, make, model):
        self.make = make
        self.model = model
        # This attribute has a default value and doesn't need a parameter.
        self.odometer_reading = 0

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📦 Creating and Using Objects

Creating an Object (Instantiation)

To create an object, you call the class name as if it were a function, providing arguments for the __init__ parameters.

# Create two separate Dog objects from the Dog class blueprint.
my_dog = Dog("Fido", 5)
your_dog = Dog("Lucy", 3)

Accessing Attributes

Use dot notation (.) to get the value of an object's attribute.

print(f"My dog's name is {my_dog.name}.") # My dog's name is Fido.
print(f"Your dog is {your_dog.age} years old.") # Your dog is 3 years old.

Modifying Attributes

You can change an attribute's value directly.

my_dog.age = 6
print(f"My dog is now {my_dog.age} years old.") # My dog is now 6 years old.

Calling Methods

Use dot notation with parentheses to call an object's method.

my_dog.bark() # Fido says: Woof!
your_dog.bark() # Lucy says: Woof!

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⚡ Quick Reference

Term	Syntax	Description
Class Definition	class ClassName:	The blueprint for your objects.
Constructor	def __init__(self, p1, p2):	Special method to set up new objects.
Attribute	self.attribute = value	A variable that belongs to the object.
Method	def method_name(self, p1):	A function that belongs to the object.
Object Creation	my_object = ClassName(a1, a2)	Creating an instance of a class.
Access Attribute	my_object.attribute	Get the value of an attribute.
Call Method	my_object.method_name(a1)	Execute a method.

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🎯 Common Mistakes to Avoid

❌ Forgetting self as the first parameter in a method.

class Player:
    # Wrong: bark() is missing 'self'.
    def bark(name): # This will cause a TypeError when called.
        print(f"{name} barks.")

✅ Always include self as the first parameter.

class Player:
    # Correct
    def bark(self, name):
        print(f"{name} barks.")

❌ Forgetting to use self. to access attributes inside a method.

class Dog:
    def __init__(self, name):
        self.name = name
    
    # Wrong: 'name' is not defined here. It should be 'self.name'.
    def greet(self):
        print(f"Hello, my name is {name}.") # NameError

✅ Always use self. to access the object's own attributes.

class Dog:
    def __init__(self, name):
        self.name = name
    
    # Correct
    def greet(self):
        print(f"Hello, my name is {self.name}.")

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Happy coding! 🐍✨