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Python - Object and Classes
On This Page
What are Classes and Objects?
Defining Classes
Example
Class Attributes
Example
Class Constructor
Example
Built-In Class Attributes
Example
Class Methods
Example
Static Methods
Example
Destroying Objects (Garbage Collection)
Example
In the Object-Oriented Programming (OOP), classes and objects are fundamental concepts that facilitate the creation of structured, modular, and maintainable code. Understanding how to effectively utilize classes and objects is essential for any Python developer aiming to build scalable and robust applications.
What are Classes and Objects?
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Classes: A class in Python acts as a blueprint for creating objects. It encapsulates data for the object and methods to manipulate that data. A class defines attributes and the behavior of its objects, as if it were sketching out the characteristics and capabilities of those objects.
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Objects: An object is an instance of a class. Defining a class creates the class itself, but no object of that class exists until you create one by calling the class. Objects are instances that are constructed following the structure of their class template and can have data and behavior as defined by the class.
Defining Classes
Defining a class in Python starts with the class keyword followed by the class name and a colon. Inside the class, methods and attributes are defined to specify the capabilities and data of the objects.
Example
In this example, we will define a simple class Dog with some basic methods.
Explanation:
class Dog:declares a new class namedDog.speak(self): An instance method that allows the dog to "speak", or rather, return a string of what the dog would say.- Creating a
Dogobject namedmy_dogdemonstrates how to instantiate objects of the classDog.
Class Attributes
Class attributes are variables defined directly in the class that are shared by all instances of the class. They can be useful for storing constants and default values that should be the same for every instance.
Example
In this example, we will define a class attribute in the Dog class that identifies the species.
Explanation:
species = "Canine": A class attribute that is shared among all instances of theDogclass, defining all dogs as belonging to the "Canine" species.print(Dog.species): Demonstrates accessing a class attribute using the class name itself rather than an instance, highlighting that this attribute is shared across all instances.
Class Constructor
In Python, the class constructor is the method that is automatically invoked when a new object is created. It is defined using the __init__ method. This method is crucial as it allows for the initialization of attributes in new objects.
Example
In this example, we will cover the constructor of the Dog class to initialize its attributes.
Explanation:
class Dog:: Defines a class calledDog.def __init__(self, name, age):The constructor method that sets up thenameandagewhen a newDogobject is created.self.name = nameandself.age = age: Assign the values passed to the constructor to thenameandageattributes of the object.puppy = Dog("Rex", 2): Creates a new instance ofDognamedpuppy.- The
printstatement confirms that the attributes have been initialized correctly.
Built-In Class Attributes
Python provides several built-in attributes for classes that provide information about the class structure. These include __dict__, __doc__, __name__, __module__, and __bases__, which can be used for introspection and are very useful in more advanced Python applications.
Example
In this example, we will explore some built-in attributes of the Dog class.
Explanation:
Dog.__doc__: Accesses the class's documentation string, which is a brief description of the class.Dog.__name__: Retrieves the name of the class.Dog.__module__: Displays the name of the module in which the class was defined.
Class Methods
Class methods are methods that are bound to the class rather than its object. They can modify the class state that applies across all instances of the class, rather than individual object instances. To define a class method in Python, you use the @classmethod decorator.
Example
In this example, we will implement a class method in the Dog class to keep track of the total number of dogs.
Explanation:
total_dogs = 0: A class attribute that keeps a count of how manyDoginstances have been created.Dog.total_dogs += 1: Increments thetotal_dogscounter each time a newDoginstance is initialized.@classmethod: Decorator that specifiesget_total_dogsas a class method.def get_total_dogs(cls): Defines a class method that returns thetotal_dogscount. It usesclsto refer to the class.- The
printstatement outputs the total number ofDoginstances, demonstrating how class methods can be used to access class-wide data.
Static Methods
Static methods are used when functionality is related to a class but does not need to access any class-specific data nor its instance data. Static methods are defined with the @staticmethod decorator and do not receive an implicit first argument (neither self nor cls).
Example
In this example, we will define a static method in the Dog class that provides a general utility unrelated to the specific attributes of any instance.
Explanation:
@staticmethod: Indicates thatis_dog_friendlyis a static method.def is_dog_friendly(): A method that returnsTrue, indicating dogs are friendly. It does not interact with class or instance data.- The
printstatement uses the class name to access the static method, illustrating that static methods can be accessed either through the class or its instances but operate independently of both.
Destroying Objects (Garbage Collection)
In Python, objects are automatically destroyed when they are no longer needed. In CPython, each object keeps a count of the references to it, and the object is freed as soon as that count drops to zero. A separate garbage collector also runs from time to time to free groups of objects that refer only to each other (reference cycles).
Example
In this example, we'll discuss how Python handles object destruction.
Explanation:
__init__(self, name): Initializes newDogobjects with a name and prints a message.__del__(self): This is the destructor method. It gets called when an object is about to be destroyed and prints a message indicating this.del my_dog: Deletes the namemy_dog. This removes the last reference to the object, so CPython destroys it right away and calls__del__.gc.collect(): Runs the cycle garbage collector by hand. In this example the object is already destroyed before this line runs, so the call is not needed. It matters only for objects caught in reference cycles.
The examples provided explore the various aspects of class-related functionalities in Python, emphasizing how different types of methods and automatic garbage collection support efficient and clear object-oriented programming. These concepts are pivotal for creating well-structured OOP applications in Python.
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On This Page
What are Classes and Objects?
Defining Classes
Example
Class Attributes
Example
Class Constructor
Example
Built-In Class Attributes
Example
Class Methods
Example
Static Methods
Example
Destroying Objects (Garbage Collection)
Example