On Fri, 17 Jun 2005 20:00:39 -0400, Roy Smith <[EMAIL PROTECTED]> wrote:
>This sounds like a very C++ view of the world. In Python, for example, >exceptions are much more light weight and perfectly routine. The problem with exceptions is coping with partial updatd state. Suppose you call a complex computation routine (say a boolean operation between winged edge data structures representing nurbs boundary of two solids) and that you get back a "ZeroDivision" exception... how good is the data structure now ? Either you have some way to be able to easily *guarantee* coherence or you're doomed. Allowing the user to continue without being sure about what is in memory is not going to be that helpful; the result could be that instead of losing last ten minuts you're going to waste the last month of user work (because the user will save the corrupted data and will notice problems only much later). If however you can restore the situation by a rollback or by loading a preimage, or you know that the operation works only *reading* two solids and creating a new one *and* you know that it's not a problem to drop a broken solid data structure then I think it's ok to swallow an exception. IMO either you know exactly what caused the exception and how the state got influenced, or you must have thick logical walls protecting you and allowing the problem to not propagate (for example an RDBMS rollback facility). With python it's sort of easy to get rollback for class instances if the code to protect doesn't plays strange tricks. Even C++ is powerful enough to allow that. With C++ care must be taken to just avoid memory leaks or other resource related problem while in python this is rarely a problem; but the real issue with exception is partial state update and in this python is not different. If you really have to check every place for possible exceptions then the exception machinery is not such a big win compared to return codes. IMO exceptions are nice when there are many raise and few try or except in the code; but then either you have state protection or swallowing an exception is taboo. Andrea -- http://mail.python.org/mailman/listinfo/python-list
