The root class for exceptions. All built-in exceptions are derived from this class. All user-defined exceptions should also be derived from this class, but this is not (yet) enforced. The str function, when applied to an instance of this class (or most derived classes) returns the string value of the argument or arguments, or an empty string if no arguments were given to the constructor. When used as a sequence, this accesses the arguments given to the constructor (handy for backward compatibility with old code). The arguments are also available on the instance’s args attribute, as a tuple.