On Fri, 28 May 2010 07:42:30 am Alex Hall wrote:
> Thanks for all the explanations, everyone. This does make sense, and
> I am now using the
> if(arg==None): arg=self.arg
> idea. It only adds a couple lines, and is, if anything, more explicit
> than what I was doing before.
You should use "if arg is None" rather than an equality test.
In this case, you are using None as a sentinel value. That is, you want
your test to pass only if you actually receive None as an argument, not
merely something that is equal to None.
Using "arg is None" as the test clearly indicates your intention:
The value None, and no other value, is the sentinel triggering special
behaviour
while the equality test is potentially subject to false positives, e.g.
if somebody calls your code but passes it something like this:
class EqualsEverything:
def __eq__(self, other):
return True
instead of None.
--
Steven D'Aprano
_______________________________________________
Tutor maillist - Tutor@python.org
To unsubscribe or change subscription options:
http://mail.python.org/mailman/listinfo/tutor
