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Python Classes and Objects for Beginners: OOP Basics with Simple Examples

P11.2 How to Add Methods to a Python Class

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Why. Data and the actions on it belong together. account.deposit(100) is clearer than a loose function.

What. A method is a function written inside the class. It uses self to read and change the object's attributes.

How.

Add a method

  1. Inside the class, write def name(self, ...):.
  2. Use self.attribute to read or update data.
  3. Call it as obj.name(...).

Worked example A — Deposit and withdraw.

Step 1 — What we do. We add actions to the account.

Step 2 — Type and run this code.

class Account:
    def __init__(self, holder, balance=0):
        self.holder = holder
        self.balance = balance

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

    def withdraw(self, amount):
        if amount > self.balance:
            print("Not enough money")
        else:
            self.balance -= amount

a = Account("Emma", 500)
a.deposit(200)
a.withdraw(1000)
a.withdraw(300)
print(a.balance)

Step 3 — Output you should see.

Not enough money
400

Step 4 — What it means. 500 + 200 = 700; the 1000 withdrawal is refused; 700 - 300 = 400.

Worked example B — A method that returns text.

Step 1 — What we do. We add a nice summary using an f-string, for a shop order.

Step 2 — Type and run this code.

class Order:
    def __init__(self, order_id, amount, currency="₹"):
        self.order_id = order_id
        self.amount = amount
        self.currency = currency

    def summary(self):
        return f"{self.order_id}: {self.currency}{self.amount:,.2f}"

print(Order("BLK-1001", 1450).summary())
print(Order("NY-77", 89.5, "$").summary())

Step 3 — Output you should see.

BLK-1001: ₹1,450.00
NY-77: $89.50

Step 4 — What it means. The same method works for every object, with its own data.

Ravindra Bagale's Tip

When you write df.head() or text.upper(), you are calling a method on an object. Now you know where the dot comes from.