Learning Python Classes and Objects by Building a Bank Account System

As I continue my Python learning journey, I recently reached one of the concepts I was really looking forward to: Classes and Objects.

At first, terms like class, object, instance, method, and self felt a little confusing.

So instead of only reading about them, I decided to build something practical:

🏦 A Bank Account Management System

This project helped me understand how classes and objects actually work in a real program.

So, what is a class?

The simplest way I can explain it is:

A class is a blueprint.

Imagine a bank has a standard design for every customer account.

Every account might have:

• An owner
• A balance
• A way to deposit money
• A way to withdraw money
• A way to check the balance
• A way to transfer money

We can represent that structure using a Python class:

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

The class describes what a bank account should have and what it should be able to do.

Then what is an object?

An object is an actual instance created from the class.

For example:

account1 = BankAccount("Israel", 10000)
account2 = BankAccount("John", 5000)

Here, BankAccount is the class, while account1 and account2 are objects.

Both objects were created from the same blueprint, but they have different data.

print(account1.owner)
# Israel

print(account2.owner)
# John

This was one of the moments where the concept really started to make sense to me.

Understanding self

One thing I had to spend time understanding was self.

When I write:

self.owner = owner
self.balance = balance

self refers to the specific object currently being worked with.

So when I do:

account1.deposit(20000)

Python knows that self refers to account1.

And when I do:

account2.deposit(2000)

self refers to account2.

That means each object can maintain its own data.

Adding methods

I then added methods to make the bank account actually useful.

For example, the deposit() method:

def deposit(self, amount):
    if amount <= 0:
        raise ValueError("Invalid amount")
    else:
        self.balance += amount
        return f"Deposit of {amount} made. New balance is {self.balance}"

I also created methods for:

• Depositing money
• Withdrawing money
• Checking the balance
• Transferring money between accounts

The transfer method was especially interesting:

def transfer(self, account, amount):
    if amount <= 0:
        raise ValueError("Invalid amount")
    elif amount > self.balance:
        return "Insufficient funds"
    else:
        self.balance -= amount
        account.balance += amount
        return f"The sum of {amount} has been transferred to {account.owner}'s account"

This helped me understand that objects can interact with other objects.

For example:

account1.transfer(account2, 3000)

Here:

• self → account1
• account → account2
• amount → 3000

So Python subtracts the money from one account and adds it to the other.

I also practiced error handling

I used raise ValueError to prevent invalid transactions.

For example:

try:
    account1.deposit(-500)
except ValueError as error:
    print(error)

This helped reinforce something I had previously learned about Python error handling.

I also learned the difference between returning a message and raising an exception.

For example:

return "Insufficient funds"

means the method returns a normal value.

While:

raise ValueError("Invalid amount")

means an exception has occurred and needs to be handled.

What I learned from this project

This project helped me understand several important Python concepts:

✅ Classes and objects
✅ __init__()
✅ Instance attributes
✅ Methods
✅ self
✅ Creating multiple objects from one class
✅ Objects interacting with other objects
✅ return inside methods
✅ raise ValueError
✅ try and except
✅ Basic Object-Oriented Programming

The biggest lesson for me was that learning programming becomes much easier when I build something instead of only watching tutorials.

I'm still learning and I definitely have more to understand about Object-Oriented Programming, but building this project made classes and objects much less intimidating.

Next, I'll continue building more projects and gradually move into more advanced OOP concepts.

One project at a time. One concept at a time.