Why custom exceptions are needed in Python - See It in Action

Why Custom Exceptions Are Needed

📖 Scenario: Imagine you are building a simple banking app. You want to handle errors like trying to withdraw more money than the account has. Python has built-in errors, but sometimes you want to create your own special error messages that make it clear what went wrong in your app.

🎯 Goal: You will create a custom exception called InsufficientFundsError to show a clear message when someone tries to take out too much money from their bank account.

📋 What You'll Learn

Create a custom exception class called InsufficientFundsError that inherits from Exception.

Create a variable balance with the value 100.

Create a variable withdraw_amount with the value 150.

Write an if statement to check if withdraw_amount is greater than balance.

If it is, raise the InsufficientFundsError with the message 'Not enough money in your account.'.

If not, subtract withdraw_amount from balance.

Print the remaining balance.

💡 Why This Matters

🌍 Real World

Custom exceptions are used in real apps to give clear error messages that help users and developers understand problems quickly.

💼 Career

Knowing how to create and use custom exceptions is important for writing clean, maintainable code in software development jobs.

1

Create the custom exception class

Create a custom exception class called InsufficientFundsError that inherits from Exception.

Python

# Your code here

Need a hint?

Use class InsufficientFundsError(Exception): and inside write pass.

2

Set up the balance and withdraw amount

Create a variable called balance and set it to 100. Then create a variable called withdraw_amount and set it to 150.

Python

class InsufficientFundsError(Exception):
    pass

# Your code here

Need a hint?

Write balance = 100 and withdraw_amount = 150.

3

Check if withdrawal is possible and raise exception

Write an if statement to check if withdraw_amount is greater than balance. If it is, raise the InsufficientFundsError with the message 'Not enough money in your account.'. Otherwise, subtract withdraw_amount from balance.

Python

class InsufficientFundsError(Exception):
    pass

balance = 100
withdraw_amount = 150

# Your code here

Need a hint?

Use if withdraw_amount > balance: then raise InsufficientFundsError('Not enough money in your account.'). Else subtract.

4

Print the remaining balance

Write print(balance) to display the remaining balance after the withdrawal check.

Python

class InsufficientFundsError(Exception):
    pass

balance = 100
withdraw_amount = 150

if withdraw_amount > balance:
    raise InsufficientFundsError('Not enough money in your account.')
else:
    balance -= withdraw_amount

# Your code here

Need a hint?

Just write print(balance). But since withdrawal is too big, the program will raise the custom error instead of printing.