Python classes and objects

Class → Definition

A class is a blueprint for creating objects that define a set of attributes and methods.

Object → Definition

An object is an instance of a class, containing data and behavior defined by the class.

True or False: Classes can contain variables.

True - Classes can have attributes (variables) that store data relevant to the object.

Constructor → Purpose

A constructor initializes an object's attributes when it is created, typically using the __init__ method.

Fill in the blank: An object is created using the ______ operator.

An object is created using the instantiation operator.

Instance vs Class Variable

Instance variables are unique to each object, while class variables are shared among all instances.

Define encapsulation.

Encapsulation is a principle of bundling data and methods that operate on that data within one unit, restricting access to some components.

Method → Definition

A method is a function defined within a class that operates on instances of that class.

Example of a simple class.

class Car: def __init__(self, make, model): self.make = make self.model = model

True or False: You can create multiple objects from one class.

True - Multiple objects can be instantiated from the same class, each with unique attributes.

Attribute → Definition

An attribute is a variable that belongs to a class or an object, holding data related to that class.

Question: Why use classes?

Classes promote organization, code reuse, and encapsulation of data and behavior.

Class vs Object

A class is a blueprint, while an object is a specific instance of that blueprint.

Constructor Example.

class Person: def __init__(self, name): self.name = name

Inheritance → Definition

Inheritance allows a class to inherit attributes and methods from another class, promoting code reuse.

Usage of 'self' in methods.

'self' refers to the instance of the class, allowing access to its attributes and methods.

Attribute → Definition

An attribute is a variable that belongs to a class. It holds the state or data of an object created from the class.

What is a method?

A method is a function defined within a class that describes the behaviors of the objects created from that class.

True or False: Methods can access class attributes.

True. Methods can access and modify attributes using the 'self' keyword to refer to the instance.

Fill in the blank: An instance variable is defined with the prefix ___

'self.' indicating that it belongs to an instance of the class.

How to define a class attribute?

Class attributes are defined directly within the class body, outside of any methods: class MyClass: class_attribute = 'value'

What does 'self' refer to?

'self' refers to the instance of the class itself within instance methods, allowing access to its attributes and methods.

Method vs. Function

A method is a function that is associated with an object. Functions can exist independently, while methods are bound to class instances.

Constructor → Purpose

The constructor method __init__ initializes new objects, setting the initial state using passed arguments.

Example of a simple method.

class Dog: def bark(self): return 'Woof!' Here, 'bark' is a method of the Dog class.

How to call a method?

To call a method, use the syntax: instance_name.method_name(). For example, dog_instance.bark().

Difference between instance and class attributes.

- Instance attributes are unique to each instance. - Class attributes are shared among all instances.

What is a property?

A property is a special type of attribute that uses getter/setter methods for controlled access and modification.

How to access an attribute?

Attributes can be accessed using dot notation: instance_name.attribute_name.

True or False: Attributes can only be strings.

False. Attributes can be of any data type including integers, lists, and even other objects.

Define a private attribute.

Private attributes are prefixed with '__', making them inaccessible from outside the class. Example: __private_attr.

What is a static method?

A static method does not modify or access instance data. It is defined with @staticmethod decorator.

Example of using 'self' in a method.

class Car: def __init__(self, make): self.make = make In this example, 'self.make' refers to the instance variable.

How to define an instance method?

An instance method is defined with at least one parameter: 'self'. For example: def instance_method(self):.

What happens if an attribute is not defined?

Accessing an undefined attribute results in an AttributeError. Always ensure attributes are initialized.

What is an attribute in a class?

An attribute is a variable that belongs to a class. - Stores data related to an object. - Can be instance or class attributes. - Example: `self.balance` in a `BankAccount` class.

Inheritance in Python

Inheritance allows one class to inherit attributes and methods from another class, promoting code reuse.

What is a base class?

A base class is the class from which other classes inherit properties and methods.

True or False: Subclasses can override base class methods.

True. Subclasses can provide a new implementation of a method defined in the base class.

What is a subclass?

A subclass is a class that derives from a base class, inheriting its features.

Fill in the blank: A subclass is also known as a ___ class.

Derived.

Multi-level inheritance

Multi-level inheritance occurs when a class inherits from another subclass, forming a hierarchy.

Polymorphism definition

Polymorphism allows methods to do different things based on the object calling them.

Example of polymorphism

Consider the method `speak()` in classes `Dog` and `Cat`. Each class implements `speak()` differently.

What is method overriding?

Method overriding occurs when a subclass provides a specific implementation of a method that is already defined in its base class.

True or False: Polymorphism only applies to classes.

False. Polymorphism can also apply to functions and data types.

Comparison: Inheritance vs Composition

- Inheritance: 'is-a' relationship. - Composition: 'has-a' relationship.

What is the `super()` function?

`super()` is used to call a method from the base class in a subclass.

Cause → Effect: Use of inheritance

Cause: Code reuse through inheritance. Effect: More maintainable and organized code.

Abstract classes

An abstract class cannot be instantiated and may contain abstract methods that must be implemented by subclasses.

Example of an abstract method

In an abstract class `Shape`, the method `area()` is an abstract method that must be defined in derived classes.

What is duck typing?

Duck typing allows an object to be used based on its methods and properties rather than its actual type.

Encapsulation in inheritance

Encapsulation restricts access to certain attributes and methods, even when inherited.

True or False: Python supports multiple inheritance.

True. Python allows a class to inherit from multiple classes.

Dynamic dispatch

Dynamic dispatch refers to the method resolution that occurs at runtime based on the object type.

What is overriding?

Overriding allows a subclass to provide a specific implementation of a method already defined in its superclass.

What is a class method?

A class method is a method that is bound to the class rather than its instance. It uses the @classmethod decorator. It receives the class as its first argument, typically named 'cls'.

True or False: Class methods can modify class state.

True. Class methods can access and modify class state that applies across all instances.

What is a static method?

A static method does not receive an implicit first argument (neither self nor cls). It is defined using the @staticmethod decorator and behaves like a regular function.

Compare class methods and static methods.

Class methods: operate on class level, receive 'cls'. Static methods: operate independently, no 'self' or 'cls'.

Fill in the blank: The ______ method is used to access an object's attributes directly.

The property method is used to access an object's attributes directly.

How to define a property?

Use the @property decorator to define a method as a property. This allows controlled access to an attribute.

What is the purpose of the @property decorator?

The @property decorator is used to define a method that can be accessed like an attribute, enabling encapsulation.

True or False: Properties can have setters and getters.

True. Properties can have both getters and setters defined using @property and @attribute_name.setter.

Cause → Effect: Using properties in a class.

Using properties increases data encapsulation and allows validation without changing the interface.

Show an example of a class method.

Example: ```python class MyClass: count = 0 @classmethod def increment_count(cls): cls.count += 1 ```

What is the significance of the @staticmethod decorator?

Static methods do not access or modify class or instance state. They are utility functions related to the class.

Fill in the blank: The ______ method allows us to define behavior for when an attribute is set.

The setter method allows us to define behavior for when an attribute is set.

How does a getter work?

A getter retrieves the value of a private attribute. It's defined using the @property decorator.

True or False: You can override properties in subclasses.

True. Properties can be overridden in subclasses, allowing for specialized behavior.

What is the purpose of static methods in a class?

Static methods provide a way to group related functions to the class, without needing an instance.

List two benefits of using class methods.

- Access to class state. - Factory methods for instance creation.