How Do I Create and Customize Exceptions in Modern Python?

How to Define Custom Exceptions in Python

Defining custom exception classes in Python has undergone changes in modern versions of the language. It's essential to follow the proper techniques to ensure compatibility and adherence to Python's conventions.

To declare a custom exception class, begin by creating a subclass of the built-in Exception class. For Python 2.6 and later, it's recommended to use the init method to initialize the exception object with custom data. Avoid using BaseException.message or Exception.args as these features are deprecated.

For instance, to define a custom exception with an error message:

class MyError(Exception):
    def __init__(self, message):
        self.message = message

To override specific behavior, you can implement methods like str__, __unicode__, and __repr for custom formatting and representation of the exception object.

Alternatively, you can pass extra arguments to the parent Exception class:

class ValidationError(Exception):
    def __init__(self, message, errors):
        super().__init__(message)
        self.errors = errors

This allows you to include additional data within the exception object, which can be accessed later. Ensure that you call the base class constructor using super().

By adhering to these conventions, you create custom exception classes that align with Python's standards and provide meaningful error handling in your applications.

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