[Tutor] Custom objects throw what exception?

[Kent Johnson]

Thanos Panousis wrote:
> The tutor list is definately helping me perform my OO-python babysteps.
> 
> I want to ask this. Say I have some objects of my own, and using the
> example I posted in a previous post, say I have a person object with a
> instance variable called hairColor.
> 
> The hairColor property is set via an exotic function that could go
> wrong and produce an exception.
> 
> How should I hanlde this? Should I catch the exception in the
> person.__init__(self,color) "construtor"? and if I do so, what happens
> the code that is waiting for a person object to arrive with a call
> like p = person(). What exception should the person class throw, if
> any?

Don't hide the exception. If you can intelligently *handle* the 
exception and create a person object that is initialized in a reasonable 
way, do so. Otherwise let some kind of exception propagate back to the 
caller so they know there is a problem.

If you catch the exception in person.__init__() then the code that calls 
person() will get whatever person object you create. The caller will not 
know that there was a problem with the color.

A ValueError might be appropriate. You can also define your own 
exception for example
   class HairColorError(Exception): pass

then in your code you can
   raise HairColorError('%s is not a valid hair color' % color)

Kent