🧩 Python OOP — Instance Methods
Introduction 🌟
An Instance Method is a function defined inside a class that operates on **instance attributes** (data belonging to a specific object). These methods always take self as their first parameter.
Note
💡 Think of an instance method as “a behavior an object can perform.”
1. Basic Example of Instance Method 🧱
basic_instance_method.py
class Person:
def greet(self): # instance method
print("Hello!")
p = Person()
p.greet()✔ Instance methods must be called using an object.
✔ self is automatically passed by Python.
2. Instance Methods with Instance Attributes 🔗
method_with_attributes.py
class Person:
def __init__(self, name):
self.name = name
def greet(self):
print(f"Hello, I'm {self.name}")
p = Person("Sathish")
p.greet()✔ Methods use instance attributes through self.
3. Instance Methods That Return Values 🎯
return_value.py
class Calculator:
def add(self, a, b):
return a + b
c = Calculator()
print(c.add(10, 20))4. Modifying Instance Attributes Inside Methods 🔧
modify_attributes.py
class BankAccount:
def __init__(self, balance):
self.balance = balance
def deposit(self, amount):
self.balance += amount
acc = BankAccount(500)
acc.deposit(200)
print(acc.balance) # 700✔ Instance methods can change the object's internal state.
5. Calling Instance Methods from Other Instance Methods 🔁
calling_methods.py
class Player:
def __init__(self, name):
self.name = name
def intro(self):
return f"Player: {self.name}"
def greet(self):
print("Welcome!", self.intro())
p = Player("Arun")
p.greet()✔ Objects can chain behaviors using instance methods.
6. Instance Methods vs Class Methods ⚔️
| Instance Method | Class Method |
|---|---|
First parameter = self | First parameter = cls |
| Works on instance data | Works on class-level data |
| Requires object to call | Can be called using class or object |
7. Example: Student System 🎒
student_instance_method.py
class Student:
def __init__(self, name, grade):
self.name = name
self.grade = grade
def details(self):
return f"{self.name} scored {self.grade}"
s = Student("Sathish", 95)
print(s.details())8. Example: Ecommerce Product 🛍️
product_example.py
class Product:
def __init__(self, title, price):
self.title = title
self.price = price
def discount(self, percent):
return self.price - (self.price * percent / 100)
p = Product("Phone", 30000)
print(p.discount(10))9. Best Practices 💡
- ✔ Always include self as the first parameter
- ✔ Keep methods focused on one purpose
- ✔ Use instance methods to manipulate instance attributes
- ✔ Use descriptive method names (verbs: run, start, add, remove)
10. Advanced Example: Password Manager 🔐
password_manager.py
class User:
def __init__(self, username, password):
self.username = username
self.password = password
def change_password(self, new_password):
self.password = new_password
print("Password updated!")
u = User("admin", "1234")
u.change_password("newpass")✔ Instance methods modify sensitive object data safely.
Conclusion 🎉
>>“Instance methods define WHAT an object can do — they give life and behavior to your classes.” ✨
You now fully understand Instance Methods in Python! Want the next topic? Try Class Methods, Static Methods, Constructors, or Inheritance. Just tell me! 😊