Coding⏱️ 2 min read📅 2026-05-30

How to Fix: How do I declare custom exceptions in modern Python

Learn how to declare custom exception classes in modern Python, following the standard for Python 2.5 and above.

Quick Answer: Use a class that inherits from the base Exception class and include any relevant data as instance variables or attributes.

To declare custom exceptions in modern Python, you should create a new exception class that inherits from the base `Exception` class. This allows you to include extra data about the cause of the error.

🛑 Root Causes of the Error

  • For example, let's create a custom exception class called `CustomError` that inherits from `Exception

🛠️ Step-by-Step Verified Fixes

Method 1: Creating a Custom Exception Class

  1. Step 1: Import the `Exception` class and create a new exception class called `CustomError

Method 2: Raising the Custom Exception

  1. Step 1: Raise the custom exception using the `raise` statement, passing in any relevant data as an argument

For example, you could raise a `CustomError` like this: raise CustomError('Something went wrong')

✨ Wrapping Up

When you catch the custom exception, you can access the extra data using the `args` attribute. For example: try:
raise CustomError('Something went wrong')
except CustomError as e:
print(e.args[0])

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❓ Frequently Asked Questions