Custom exceptions in Python

Custom exceptions in Python.md

Custom exceptions in Python

The simplest way to define a custom error in Python is as follows:

class CustomError(Exception): pass

This exception can be raised in any of the following ways:

raise CustomError("This is my error message")
raise CustomError()
raise CustomError

It is possible to pass an error message to the constructor along with other arguments, or to set a constant error message for the exception, by calling the constructor of the parent class, as described in this Stack Overflow answer:

class CustomError2(Exception):
    def __init__(self):
        super().__init__(
            "Custom error message "
            "which spans multiple lines"
        )

This exception can be raised in either of the following ways, with the custom error message being printed to the console:

raise CustomError2()
raise CustomError2