On Thu, Apr 5, 2012 at 21:57, Stephen J. Turnbull <stephen@xemacs.org> wrote:
I might have chosen to implement a 'None' return if I had designed open(), but I can't get too upset about raising an Exception as it actually does.
One fundamental difference is that there are many reasons one might fail to open a file. It may not exist. It may not have permissions allowing the request. It may be locked. If open() returned None, this information would have to be retrievable through another function. However since it returns an exception, that information is already wrapped up in the exception object, should you choose to catch it, and likely to be logged otherwise. In the case of the clocks, I'm assuming the only reason you would fail to get a clock is because it isn't provided by hardware and/or OS. You don't have to worry about transient scenarios on multi-user systems where another user has locked the clock. Thus the exception cannot tell you anything more than None tells you. (Of course, if my assumption is wrong, I'm not sure whether my reasoning still applies.) -- Michael Urman