__init__()<\/code><\/td>\nConstructor method that initializes new objects (automatically called when creating instances)<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\nConstructors (__init__)<\/h2>\nWhat Is a Constructor?<\/h3>\nA constructor is a special method in a class that’s automatically called when a new object (instance) is created.<\/p>\n In Python, this constructor method is named __init__().<\/p>\n Purpose of __init__()<\/strong><\/p>\n\n- To initialize attributes (variables) of a new object.<\/li>\n
- To ensure each object starts in a well-defined state.<\/li>\n
- To optionally accept arguments during object creation.<\/li>\n<\/ul>\n
Basic Syntax<\/strong><\/p>\nclass Person:<\/em>
\ndef __init__(self, name, age): # Constructor<\/em>
\nself.name = name<\/em>
\nself.age = age<\/em><\/p>\n\n- self: Refers to the current instance.<\/li>\n
- name, age: Parameters used to set object-specific data.<\/li>\n<\/ul>\n
Creating an Object<\/strong><\/p>\np1 = Person(“Alice”, 30)<\/em>
\nprint(p1.name) # Alice<\/em>
\nprint(p1.age) # 30<\/em><\/p>\nWhen Person(“Alice”, 30) is called:<\/strong><\/p>\n\n- Python creates a new Person object.<\/li>\n
- Calls __init__() with name=”Alice” and age=30.<\/li>\n
- Sets self.name and self.age.<\/li>\n<\/ul>\n
Default Values<\/strong><\/p>\nYou can set default values for parameters:<\/strong><\/p>\nclass Person:<\/em>
\ndef __init__(self, name=”Unknown”, age=0):<\/em>
\nself.name = name<\/em>
\nself.age = age<\/em><\/p>\nNow you can call Person() with no arguments:<\/strong><\/p>\np2 = Person()<\/em>
\nprint(p2.name, p2.age) # Unknown 0<\/em><\/p>\nPoints to Remember<\/strong><\/p>\n\n\n\n| Feature<\/th>\n | Description<\/th>\n<\/tr>\n<\/thead>\n | \n\nSpecial method<\/strong><\/code><\/td>\n__init__<\/code> is automatically called when creating a new object instance<\/td>\n<\/tr>\n\nSelf parameter<\/strong><\/code><\/td>\n| Refers to the current object instance (must be first parameter in method definition)<\/td>\n<\/tr>\n | \nInitialization<\/strong><\/code><\/td>\n| Primary purpose is to initialize the object’s attributes and state<\/td>\n<\/tr>\n | \nDefault values<\/strong><\/code><\/td>\n| Parameters can have default values to make them optional during instantiation<\/td>\n<\/tr>\n | \nNot mandatory<\/code><\/strong><\/td>\n| Can be omitted if no initialization logic is required (Python provides default)<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n Without __init__<\/strong><\/p>\nclass Empty:<\/em>
\npass<\/em><\/p>\ne = Empty()<\/em><\/p>\nThis still works \u2014 but the object won\u2019t have any initialized attributes unless added manually.<\/p>\n Summary:<\/strong><\/p>\n\n- __init__ is Python\u2019s constructor method, used to initialize object attributes.<\/li>\n
- It runs automatically when an object is created.<\/li>\n
- It makes your classes more flexible, dynamic, and useful.<\/li>\n<\/ul>\n
Instance and class variables<\/h2>\nWhat Are Instance and Class Variables?<\/strong><\/p>\nInstance Variables are variables that are specific to each instance (object) of a class.<\/p>\n Class Variables are variables that are shared across all instances of the class. These are stored at the class level and have the same value for every object of the class.<\/p>\n 1. Instance Variables<\/h3>\nWhat Are They?<\/strong><\/p>\n\n- Instance variables are unique to each object. Every time a new object is created, it can have its own values for instance variables.<\/li>\n
- They are typically initialized inside the __init__() constructor.<\/li>\n<\/ul>\n
Example<\/strong><\/p>\nclass Dog:<\/em>
\ndef __init__(self, name, age):<\/em>
\nself.name = name # instance variable<\/em>
\nself.age = age # instance variable<\/em><\/p>\ndog1 = Dog(“Buddy”, 3)<\/em>
\ndog2 = Dog(“Bella”, 5)<\/em><\/p>\nprint(dog1.name) # Buddy<\/em>
\nprint(dog2.name) # Bella<\/em><\/p>\nIn this case, name and age are instance variables because each dog object can have different values for these attributes.<\/p>\n 2. Class Variables<\/h3>\nWhat Are They?<\/strong><\/p>\n\n- Class variables are shared across all instances of the class.<\/li>\n
- They are typically defined inside the class but outside of any methods.<\/li>\n
- Class variables are often used for properties that should be common to all objects, such as a constant or counter.<\/li>\n<\/ul>\n
Example<\/strong><\/p>\nclass Dog:<\/em>
\nspecies = “Canine” # class variable<\/em><\/p>\ndef __init__(self, name, age):<\/em>
\nself.name = name # instance variable<\/em>
\nself.age = age # instance variable<\/em><\/p>\ndog1 = Dog(“Buddy”, 3)<\/em>
\ndog2 = Dog(“Bella”, 5)<\/em><\/p>\nprint(dog1.species) # Canine<\/em>
\nprint(dog2.species) # Canine<\/em><\/p>\n# Changing class variable for the class<\/em>
\nDog.species = “Dog”<\/em><\/p>\nprint(dog1.species) # Dog<\/em>
\nprint(dog2.species) # Dog<\/em><\/p>\n\n- species is a class variable because it is the same for all instances of Dog. If you change it at the class level, it changes for all instances automatically.<\/li>\n<\/ul>\n
Differences Between Instance and Class Variables<\/strong><\/p>\n\n\n\n| Feature<\/th>\n | Instance Variables<\/th>\n | Class Variables<\/th>\n<\/tr>\n<\/thead>\n | \n\nScope<\/strong><\/td>\n| Unique to each object instance<\/td>\n | Shared among all instances of the class<\/td>\n<\/tr>\n | \nInitialization<\/strong><\/td>\nDefined in __init__()<\/code> method using self<\/code><\/td>\n| Defined directly in class body (outside methods)<\/td>\n<\/tr>\n | \nAccess<\/strong><\/td>\nAccessed via self.<variable_name><\/code><\/td>\nAccessed via ClassName.<variable_name><\/code> or self.<variable_name><\/code><\/td>\n<\/tr>\n\nUsage<\/strong><\/td>\n| Stores object-specific data (unique state)<\/td>\n | Stores class-level data (shared state)<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n3. Modifying Class Variables<\/h3>\nClass variables can be accessed and modified using the class name or instance:<\/p>\n class Dog:<\/em>
\nspecies = “Canine” # class variable<\/em><\/p>\ndog1 = Dog(“Buddy”, 3)<\/em>
\ndog2 = Dog(“Bella”, 5)<\/em><\/p>\nprint(dog1.species) # Canine<\/em><\/p>\n# Changing class variable using the class name<\/em>
\nDog.species = “Dog”<\/em><\/p>\nprint(dog1.species) # Dog<\/em>
\nprint(dog2.species) # Dog<\/em><\/p>\nWarning:<\/strong><\/p>\nModifying a class variable using an instance (e.g., dog1.species = “New species”) will create an instance variable with that name, effectively shadowing the class variable.<\/p>\n Summary:<\/strong><\/p>\n\n- Instance Variables: Unique to each object; defined inside the __init__() method using self.<\/li>\n
- Class Variables: Shared by all objects of the class; defined directly in the class body.<\/li>\n<\/ul>\n
Inheritance and polymorphism<\/h2>\nWhat Is Inheritance?<\/h3>\nInheritance is a way to allow a new class (child class) to inherit attributes and methods from an existing class (parent class). This promotes code reuse and allows for creating more specialized classes based on general ones.<\/p>\n Key Concepts:<\/strong><\/p>\n\n- Parent Class (or Base Class): The class being inherited from.<\/li>\n
- Child Class (or Derived Class): The class that inherits from the parent class.<\/li>\n<\/ul>\n
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