On Aug 30, 1:27 am, Marc 'BlackJack' Rintsch <[EMAIL PROTECTED]> wrote: > On Thu, 30 Aug 2007 17:09:36 +1000, Ben Finney wrote: > > [EMAIL PROTECTED] writes: > > >> What's with the index() function of lists throwing an exception on not > >> found? > > > It's letting you know that the item isn't in the list. There's no > > sensible return value from an "index" function in that condition. > > What about -1? C programmers do this all the time. :-) > > Ciao, > Marc 'BlackJack' Rintsch
As other people pointed out, C doesn't have exceptions, so a C programmer must make an in/out parameter to indicate an error, or have a special return value. In Python, you're most often searching the list for an object which is in the list, so the lack of the object is an exceptional condition. You can certain check with the "in" operator beforehand to avoid the exception. You may also subclass a list and override the index method, or write a standalone function to catch the exception and change its value. The reason why the exception is more Pythonic is that the return value is always a guaranteed good index into the list. Any errors (including calling .index() on a non-list instance that doesn't have a .index method) are exceptional, and should probably follow a very different code path. Returning -1 is not a good return value to indicate an error. After all, -1 is a valid index in most Python lists. (Negative numbers index from the tail of the list.) --Jason -- http://mail.python.org/mailman/listinfo/python-list
