__init__ in Python

Prerequisites – Python Class and Objects, Self

__init__ method in Python is used to initialize objects of a class. It is also called a constructor. It is like a default constructor in C++ and Java. Constructors are used to initialize the object’s state.

The task of constructors is to initialize (assign values) to data members of the class when an object of the class is created. Like methods, a constructor also contains a collection of statements(i.e. instructions) that are executed at the time of Object creation. It is run as soon as an object of a class is instantiated.

# A Sample class with init method
class Person:

    # init method or constructor
    def __init__(self, name):
        self.name = name

    # Sample Method
    def say_hi(self):
        print('Hello, my name is', self.name)


p = Person('Nikhil')
p.say_hi()

Output:

Hello, my name is Nikhil

Understanding the code

• In the above example, a person named Nikhil is created. While creating a person, “Nikhil” is passed as an argument, this argument will be passed to the __init__ method to initialize the object.
• The keyword self represents the instance of a class and binds the attributes with the given arguments. Similarly, many objects of the Person class can be created by passing different names as arguments.

__init__ with Parameter

# A Sample class with init method
class Person:

    # init method or constructor
    def __init__(self, name):
        self.name = name

    # Sample Method
    def say_hi(self):
        print('Hello, my name is', self.name)


# Creating different objects
p1 = Person('Nikhil')
p2 = Person('Abhinav')
p3 = Person('Anshul')

p1.say_hi()
p2.say_hi()
p3.say_hi()

Output:

Hello, my name is Nikhil
Hello, my name is Abhinav
Hello, my name is Anshul

__init__ Method with Inheritance

Inheritance is the capability of one class to derive or inherit the properties from some other class. Let’s consider the below example to see how __init__ works in inheritance. 

# Python program to
# demonstrate init with
# inheritance

class A(object):
    def __init__(self, something):
        print("A init called")
        self.something = something


class B(A):
    def __init__(self, something):
        # Calling init of parent class
        A.__init__(self, something)
        print("B init called")
        self.something = something


obj = B("Something")

Output:

A init called
B init called

So, the parent class constructor is called first. But in Python, it is not compulsory that the parent class constructor will always be called first.

The order in which the __init__ method is called for a parent or a child class can be modified. This can simply be done by calling the parent class constructor after the body of the child class constructor. 

Example: 

# Python program to
# demonstrate init with
# inheritance

class A(object):
    def __init__(self, something):
        print("A init called")
        self.something = something


class B(A):
    def __init__(self, something):
        print("B init called")
        self.something = something
        # Calling init of parent class
        A.__init__(self, something)


obj = B("Something")

Output:

B init called
A init called

Read: Inheritance in Python

Related Article

• Is __init__() a private method in Python?
• What is the difference between __init__ and __call__?
• __new__ in Python

__init__ in Python – FAQs

What is the __init__ Method in Python?

The __init__ method in Python is a special method called a constructor. It is automatically invoked when a new instance (object) of a class is created. The purpose of the __init__ method is to initialize the object’s attributes and perform any other setup necessary when an object is instantiated.

How is __init__ Used in Python Classes?

The __init__ method is defined within a class and typically includes the self parameter, which refers to the instance being created, followed by any other parameters needed to initialize the object.

Example:

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

# Creating an instance of the Person class
person = Person("Alice", 30)
print(person.name)  # Output: Alice
print(person.age)   # Output: 30

In this example, the __init__ method initializes the name and age attributes of the Person class.

What are Constructors in Python?

Constructors in Python are special methods used to initialize newly created objects. The __init__ method is the constructor in Python. It allows you to set up the initial state of an object by assigning values to its attributes or performing other setup tasks.

How to Initialize a New Object in Python?

To initialize a new object in Python, you create an instance of a class, which automatically invokes the __init__ method.

Example:

class Dog:
    def __init__(self, name, breed="Mixed", age=1):
        self.name = name
        self.breed = breed
        self.age = age

# Creating an instance with default parameters
dog1 = Dog("Buddy")
print(dog1.name)   # Output: Buddy
print(dog1.breed)  # Output: Mixed
print(dog1.age)    # Output: 1

# Creating an instance with specified parameters
dog2 = Dog("Max", "Golden Retriever", 5)
print(dog2.name)   # Output: Max
print(dog2.breed)  # Output: Golden Retriever
print(dog2.age)    # Output: 5

What are the Default Parameters in __init__?

The __init__ method can include default parameter values. This allows you to create objects with default attribute values if no arguments are provided for those parameters.

Example:

class Dog:
    def __init__(self, name, breed="Mixed", age=1):
        self.name = name
        self.breed = breed
        self.age = age

# Creating an instance with default parameters
dog1 = Dog("Buddy")
print(dog1.name)   # Output: Buddy
print(dog1.breed)  # Output: Mixed
print(dog1.age)    # Output: 1

# Creating an instance with specified parameters
dog2 = Dog("Max", "Golden Retriever", 5)
print(dog2.name)   # Output: Max
print(dog2.breed)  # Output: Golden Retriever
print(dog2.age)    # Output: 5

In this example, the breed and age parameters have default values. If these parameters are not provided when creating a Dog object, the default values will be used.

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Article Tags :

• Python
• Python-OOP

Practice Tags :

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