init is a special method in Python that initializes a new instance of a class. It automatically runs when an object is created, setting up initial attributes and state. The first parameter, self, refers to the instance, and additional parameters can be used to pass data. Default values can be assigned for optional parameters, and setup logic like validation or initializing containers can also be included. For example, in a Person class, init can set name and age, while in a BankAccount class, it can validate balance.
The __init__ method in a Python class is a special method that gets called automatically when you create a new instance of the class. It's used to initialize the object’s attributes and set up the initial state. You don't need to call it explicitly — Python handles that for you during object creation.
What is __init__?
__init__ stands for "initialize." It's not a constructor in the traditional sense (that role belongs to __new__), but it's where you typically assign values to instance variables.
When you create an object like obj = MyClass(), Python creates the instance and then calls __init__ on it, passing any arguments you provided.
Basic Syntax and Usage
Here’s how to define __init__ inside a class:
- The first parameter must be self, which refers to the instance being created.
- Additional parameters can be added to pass data during instantiation.
- You assign values to self.attribute_name to store them in the instance.
class Person:
???def init(self, name, age):
??????self.name = name
??????self.age = age
Creating instances
person1 = Person("Alice", 30)
person2 = Person("Bob", 25)
print(person1.name, person1.age) # Output: Alice 30
print(person2.name, person2.age) # Output: Bob 25
Setting Default Values
You can give parameters default values if they’re optional:
class Dog:???def __init__(self, name, breed="Unknown"):
??????self.name = name
??????self.breed = breed
dog1 = Dog("Buddy")
dog2 = Dog("Max", "Golden Retriever")
print(dog1.breed) # Output: Unknown
print(dog2.breed) # Output: Golden Retriever
Running Setup Code
Besides assigning attributes, __init__ can run other setup logic like validation, logging, or initializing containers:
class BankAccount:???def __init__(self, owner, balance=0):
??????self.owner = owner
??????self.balance = balance
??????if balance ?????????raise ValueError("Balance cannot be negative")
account = BankAccount("John", 100)
Basically, use __init__ to prepare your object with the data and settings it needs right from the start. It keeps your instances consistent and ready to use after creation.
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