Custom exceptions

You don't have to rely solely on built-in exceptions like IndexError: you can define your own exceptions more specific to your application. You can also define exception hierarchies. All you need to define an exception is a class inherited from the built-in Exception class or one of its subclasses.

In Chapter 1, you defined an Employee class and used print statements and default values to handle errors like creating an employee with a salary below the minimum or giving a raise that is too big. A better way to handle this situation is to use exceptions. Because these errors are specific to our application (unlike, for example, a division by zero error which is universal), it makes sense to use custom exception classes.