Which of the following function is called when a class is used to create a new object in Python?

Python is an object-oriented programming language. Python Classes and Objects are the core building blocks of Python programming language.

Python Class

By this time, all of you should have already learned about Python Data Types. If you remember, basic data types in python refer to only one kind of data at a time. How would it be if you could declare a data type which itself contains more than one data types and can work with them with the help of any function? Python class gives you that opportunity. Python class is the blueprint on which instances of the class are created.

Simple Python Class Declaration

Here’s the very basic structure of python class definition.

Now, let’s work with real examples.

This example is pretty much self-explanatory. As we know, the lines starting with “#” are python comments. The comments explain the next executable steps. This code produces the following output.

Python Class Definition

This line marks the beginning of class definition for class ‘Person’.

Python Class Variables

‘name’ and ‘age’ are two member variables of the class ‘Person’. Every time we declare an object of this class, it will contain these two variables as its member. This part is optional as they can be initialized by the constructor.

Python Class Constructor

Python class constructor is the first piece of code to be executed when you create a new object of a class. Primarily, the constructor can be used to put values in the member variables. You may also print messages in the constructor to be confirmed whether the object has been created. We shall learn a greater role of constructor once we get to know about python inheritance. The constructor method starts with def __init__. Afterward, the first parameter must be ‘self’, as it passes a reference to the instance of the class itself. You can also add additional parameters like the way it is shown in the example. ‘personName’ and ‘personAge’ are two parameters to sent when a new object is to be created.

Python Class Methods

Methods are declared in the following way:

In the pre-stated example, we’ve seen that the method showName() prints value of ‘name’ of that object. We shall discuss a lot more about python methods some other day.

Python Class Object

The way objects are created in python is quite simple. At first, you put the name of the new object which is followed by the assignment operator and the name of the class with parameters (as defined in the constructor). Remember, the number and type of parameters should be compatible with the parameters received in the constructor function. When the object has been created, member methods can be called and member attributes can be accessed (provided they are accessible).

That’s all for the basics of python class. As we are going to learn about python object-oriented features like inheritance, polymorphism in the subsequent tutorials, we shall learn more about python class and its features. Till then, happy coding and good bye! Feel free to comment if you have any query. Reference: Python.org Documentation

A class is a user-defined blueprint or prototype from which objects are created. Classes provide a means of bundling data and functionality together. Creating a new class creates a new type of object, allowing new instances of that type to be made. Each class instance can have attributes attached to it for maintaining its state. Class instances can also have methods (defined by their class) for modifying their state.

To understand the need for creating a class in Python let’s consider an example, let’s say you wanted to track the number of dogs that may have different attributes like breed, and age. If a list is used, the first element could be the dog’s breed while the second element could represent its age. Let’s suppose there are 100 different dogs, then how would you know which element is supposed to be which? What if you wanted to add other properties to these dogs? This lacks organization and it’s the exact need for classes. 

Syntax: Class Definition 

Syntax: Object Definition

Class creates a user-defined data structure, which holds its own data members and member functions, which can be accessed and used by creating an instance of that class. A class is like a blueprint for an object.

Some points on Python class:  

• Classes are created by keyword class.
• Attributes are the variables that belong to a class.
• Attributes are always public and can be accessed using the dot (.) operator. Eg.: Myclass.Myattribute

Defining a class 

In the above example, the class keyword indicates that you are creating a class followed by the name of the class (Dog in this case).

Class Objects

An Object is an instance of a Class. A class is like a blueprint while an instance is a copy of the class with actual values. It’s not an idea anymore, it’s an actual dog, like a dog of breed pug who’s seven years old. You can have many dogs to create many different instances, but without the class as a guide, you would be lost, not knowing what information is required.
An object consists of : 

• State: It is represented by the attributes of an object. It also reflects the properties of an object.
• Behaviour: It is represented by the methods of an object. It also reflects the response of an object to other objects.
• Identity: It gives a unique name to an object and enables one object to interact with other objects.

Declaring Objects (Also called instantiating a class)

When an object of a class is created, the class is said to be instantiated. All the instances share the attributes and the behavior of the class. But the values of those attributes, i.e. the state are unique for each object. A single class may have any number of instances.

Example:

Declaring an object

Python3

class Dog:

    attr1 = "mammal"

    attr2 = "dog"

    def fun(self):

        print("I'm a", self.attr1)

        print("I'm a", self.attr2)

Rodger = Dog()

print(Rodger.attr1)

Rodger.fun()

Output

In the above example, an object is created which is basically a dog named Rodger. This class only has two class attributes that tell us that Rodger is a dog and a mammal.

The self

• Class methods must have an extra first parameter in the method definition. We do not give a value for this parameter when we call the method, Python provides it.
• If we have a method that takes no arguments, we still have one argument.
• This is similar to this pointer in C++ and this reference in Java.

When we call a method of this object as myobject.method(arg1, arg2), this is automatically converted by Python into MyClass.method(myobject, arg1, arg2) – this is all the special self is about.

__init__ method

The __init__ method is similar to constructors in C++ and Java. Constructors are used to initialize the object’s state. Like methods, a constructor also contains a collection of statements(i.e. instructions) that are executed at the time of Object creation. It runs as soon as an object of a class is instantiated. The method is useful to do any initialization you want to do with your object.

Python3

class Person:

    def __init__(self, name):

        self.name = name

    def say_hi(self):

        print('Hello, my name is', self.name)

p = Person('Nikhil')

p.say_hi()

Output: 

Class and Instance Variables

Instance variables are for data, unique to each instance and class variables are for attributes and methods shared by all instances of the class. Instance variables are variables whose value is assigned inside a constructor or method with self whereas class variables are variables whose value is assigned in the class.

Defining instance variables using a constructor. 

Python3

class Dog:

    animal = 'dog'

    def __init__(self, breed, color):

        self.breed = breed

        self.color = color

Rodger = Dog("Pug", "brown")

Buzo = Dog("Bulldog", "black")

print('Rodger details:')

print('Rodger is a', Rodger.animal)

print('Breed: ', Rodger.breed)

print('Color: ', Rodger.color)

print('\nBuzo details:')

print('Buzo is a', Buzo.animal)

print('Breed: ', Buzo.breed)

print('Color: ', Buzo.color)

print("\nAccessing class variable using class name")

print(Dog.animal)

Output

Defining instance variables using the normal method.

Python3

class Dog:

    animal = 'dog'

    def __init__(self, breed):

        self.breed = breed

    def setColor(self, color):

        self.color = color

    def getColor(self):

        return self.color

Rodger = Dog("pug")

Rodger.setColor("brown")

print(Rodger.getColor())

Which of the following function is called when a class is used to create a new object?

What is the function that gets called when a class is created?

What is the function of class in Python?

Which method is called when an object is created from a class and allows the class to initialize the attributes of the class?