{"id":3101,"date":"2021-11-28T04:13:21","date_gmt":"2021-11-28T04:13:21","guid":{"rendered":"https:\/\/www.pythontutorial.net\/?page_id=3101"},"modified":"2025-03-28T03:55:39","modified_gmt":"2025-03-28T03:55:39","slug":"python-custom-exception","status":"publish","type":"page","link":"https:\/\/www.pythontutorial.net\/python-oop\/python-custom-exception\/","title":{"rendered":"Python Custom Exception"},"content":{"rendered":"\n

Summary<\/strong>: in this tutorial, you’ll learn how to define Python custom exception classes.<\/p>\n\n\n\n

Introduction to the Python custom exception #<\/a><\/h2>\n\n\n\n

To create a custom exception<\/a> class, you define a class<\/a> that inherits<\/a> from the built-in Exception<\/code> class or one of its subclasses such as ValueError<\/code> class:<\/p>\n\n\n\n

\"Python<\/figure><\/div>\n\n\n\n

The following example defines a CustomException<\/code> class that inherits from the Exception<\/code> class:<\/p>\n\n\n

class<\/span> CustomException<\/span>(Exception)<\/span>:<\/span>\n    \"\"\" my custom exception class \"\"\"<\/span><\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Note that the CustomException<\/code> class has a docstring that behaves like a statement. Therefore, you don’t need to add the pass<\/code> statement to make the syntax valid.<\/p>\n\n\n\n
class<\/span> CustomException<\/span>(Exception)<\/span>:<\/span>\n    \"\"\" my custom exception class \"\"\"<\/span>\n\n\ntry<\/span>:\n    raise<\/span> CustomException('This is my custom exception'<\/span>)\nexcept<\/span> CustomException as<\/span> ex:\n    print(ex)<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
This is<\/span> my custom exception<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Like standard exception classes, custom exceptions are also classes. Hence, you can add functionality to the custom exception classes like:<\/p>\n\n\n\n
To raise the CustomException, you use the raise<\/a><\/code> statement. For example, the following uses the raise<\/code> statement to raise the CustomException<\/code>:<\/p>\n\n\n