Python init Method

When you create an object from a class, Python looks for a special method named __init__ and calls it right away. Its job is initialization: setting up the starting attributes of the new object. The double underscores on each side mark it as a dunder (double-underscore) method, part of a group of names Python treats specially. You never call __init__ yourself; Python invokes it for you when you create the instance.

Passing data in when you create an object

Any argument you pass when creating an object is forwarded to __init__ after self. Inside the method you store those arguments as attributes so the rest of the class can use them later.

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

    def greet(self):
        return f"Hi, I'm {self.name} and I'm {self.age}."

p = Person("Asha", 29)
print(p.greet())   # Hi, I'm Asha and I'm 29.

Default values for parameters

You can give parameters in __init__ default values so callers may leave them out. This makes objects flexible: supply everything, or accept sensible defaults for the rest.

class BankAccount:
    def __init__(self, owner, balance=0):
        self.owner = owner
        self.balance = balance

    def deposit(self, amount):
        self.balance += amount
        return self.balance

acc = BankAccount("Ravi")   # balance defaults to 0
acc.deposit(500)
print(acc.owner, acc.balance)   # Ravi 500

• __init__ is the constructor Python calls when you create an object.
• Its first parameter is always self.
• Store incoming arguments as attributes with self.attribute = value.
• Give parameters defaults to make them optional.