# Attributes (OOP) ## What is an attribute? - In object-oriented programming (OOP), an **attribute** refers to a data member or a property associated with an **object** or a **class** - Attributes define the **state** of an object and can have different values for different instances of the same class - Attributes can be of various **data types**, such as integers, strings, Booleans, or even other objects - Attributes can have different **access rights** (public or private)

An attribute is a data member that defines the state or properties of an object within a class

## Attributes and data types - When declaring an attribute, you must specify its **data type** - Common data types for attributes include: - **Integer** - for whole numbers - **Real/Float** - for decimal numbers - **String** - for text values - **Boolean** - for true/false values - **Object** - references to other objects ### Example: Book class with an attribute Consider a `Book` class object with an attribute called `title`: - It has **private** access, meaning it can only be accessed by instances of the `Book` class - The data that this attribute will hold must be of the **String** data type - When an object is instantiated with a data value of `"1984"`, that specific instance stores this value ## Class variables vs instance variables - **Class Variables**: Attributes that are defined within a class itself - Also known as **class attributes** - Shared template that defines what data each object will hold - **Instance Variables**: Attributes that belong to objects created from a class - Also known as **object attributes** - Each object has its own unique values for these attributes

Every object instantiated from a class gets its own copy of instance variables with potentially different values

## Multiple attributes in a class - In most cases, each class has many different attributes - Each attribute describes a specific property of the object ### Example: Smartphone class Consider an object of class `Smartphone`: | Attribute | Data Type | Example Value | |-----------|-----------|---------------| | brand | String | "TechCorp" | | model | String | "X500" | | storageGB | Integer | 256 | | batteryPercentage | Integer | 85 | | isUnlocked | Boolean | true | - The `brand` attribute stores which company manufactured the phone - The `model` attribute identifies the specific model variant - The `storageGB` attribute holds the storage capacity in gigabytes - The `batteryPercentage` attribute tracks current battery level - The `isUnlocked` attribute indicates whether the phone is currently unlocked ## Access modifiers for attributes Attributes can be declared with different access levels: | Access Modifier | Description | |-----------------|-------------| | **Private** | Only accessible within the class itself; external code cannot access them directly | | **Public** | Accessible and can be modified by any code within the same class or from external classes |

Private attributes provide encapsulation and protect data from unintended modification

- **Private attributes** are best practice for data security - Prevents accidental modification from outside the class - Changes can only be made through controlled methods (getters/setters) - **Public attributes** allow direct access - Convenient but less secure - Can be modified by any part of the program ### Example: Access modifiers in practice ```python class Smartphone private brand public model private storageGB ``` - The `brand` and `storageGB` attributes are **private** - only accessible within the `Smartphone` class - The `model` attribute is **public** - can be accessed from anywhere in the program ## Local variables vs attributes

Attributes declared within methods (local variables) cannot have access modifiers because they are local to the method and have limited scope

- **Local variables** are only accessible within the block or method in which they are declared - They are not part of the class's state and cannot be accessed from other methods or classes - Local variables exist only during method execution and are destroyed afterwards - Unlike class attributes, local variables don't need `public` or `private` keywords ### Comparison table | Feature | Class Attributes | Local Variables | |---------|-----------------|-----------------| | Scope | Entire class | Single method/block | | Lifetime | Entire object lifetime | Method execution only | | Access modifiers | Required (public/private) | Not allowed | | Accessibility | All methods in class | Only within declaring method |

If an attribute doesn't specify public or private, assume it is public by default

## Practical considerations - Attributes store the **state** of an object at any given moment - Different objects of the same class can have completely different attribute values - Choosing appropriate data types for attributes is crucial for memory efficiency and correctness - Using private attributes with public getter/setter methods provides controlled access to data