Instance Methods

Instance methods are functions defined within a class that operate on instances of the class. They take the instance itself as the first argument, conventionally named self. This allows the method to access and modify the instance's attributes and other methods.

Defining Instance Methods

Instance methods are defined using the def keyword inside a class. The first parameter of an instance method is always self, which refers to the instance on which the method is called.

Example:

class Car:
    def __init__(self, make, model):
        self.make = make
        self.model = model

    def display_info(self):
        return f"{self.make} {self.model}"

# Create an instance of Car
my_car = Car("Opel", "Astra")
print(my_car.display_info())  # Output: Opel Astra

Accessing and Modifying Attributes

Instance methods can access and modify instance attributes defined in the __init__ method or elsewhere in the class.

Example:

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

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

    def get_balance(self):
        return self.balance

# Create an instance of BankAccount
account = BankAccount(100)
account.deposit(50)
print(account.get_balance())  # Output: 150

Using `self`

The self parameter is used to access instance attributes and other methods from within an instance method. It is automatically passed by Python when the method is called on an instance.

Example:

class Rectangle:
    def __init__(self, width, height):
        self.width = width
        self.height = height

    def area(self):
        return self.width * self.height

    def perimeter(self):
        return 2 * (self.width + self.height)

# Create an instance of Rectangle
rect = Rectangle(4, 5)
print(rect.area())       # Output: 20
print(rect.perimeter())  # Output: 18

Best Practices

Use Descriptive Names: Name methods clearly to reflect their functionality.
Keep Methods Focused: Each instance method should have a single responsibility. Avoid making methods too complex or multi-functional.
Document Methods: Use docstrings to describe the purpose and behavior of instance methods for better code readability and maintainability.
Avoid Modifying Global State: Instance methods should generally operate on instance data rather than affecting global state or other unrelated instances.

Notes about Python