Python Programming with the Java™ Class Libraries: A Tutorial for Building Web and Enterprise Applications with Jython

The raise Statement

A raise statement forces an exception to be raised. One form is

raise exception-expression, description-expression

In our denominator example, it raises a specific exception.

>>> raise ZeroDivisionError, "Sequence has a Zero value in the denominator"
Traceback (innermost last):
  File "<stdin>", line 1, in ?
ZeroDivisionError: Sequence has a Zero value in the denominator

The exception-expression must be of type String or be an instance object. The description-expression is optional. If you use raise with no exception-expression, it reraises the last exception.

You can easily define your own exception using a string variable.

 >>> badListForm = 'badListForm' >>> try: ... raise badListForm, "The list had a malformed tuple" ...