[Tutor] am I missing another simpler structure?
cyresse at gmail.com
Thu Dec 16 07:41:24 CET 2004
I find multiple returns to be rather useful -
if not x % 2: return False
On Thu, 16 Dec 2004 01:06:58 -0500, Brian van den Broek
<bvande at po-box.mcgill.ca> wrote:
> [Brian van den Broek]
> <SNIP setup of how I was wondering if I was making things too
> complicated with:>
> >>import datetime
> >>def is_leap_year(year):
> >> '''-> boolean
> >> Returns True or False as year is, or is not, a leap year.
> >> '''
> >> is_leap = True
> >> try:
> >> datetime.date(year, 2, 29)
> >> except ValueError:
> >> is_leap = False
> >> return is_leap
> Kent Johnson said unto the world upon 2004-12-15 20:16:
> > I would write
> > def is_leap_year(year):
> > try:
> > datetime.date(year, 2, 29)
> > return True
> > except ValueError:
> > return False
> Not an adherent of the "only one exit point" doctrine then, hey? I spent
> a while a few weeks ago with a bug in a function that happened because
> I'd not noticed that I had two return statements, so I'm leery of this
> at the moment. (I concede if the function was long enough to hide that
> from me, it was probably too long.) I also like the conceptual purity of
> one way in and one way out. But, in my code above, that is indeed
> purchased at the cost of the ugly and a bit anomalous assignment of True.
> Tim Peters said unto the world upon 2004-12-15 23:14:
> > So far as leap years go, the obvious difference is that February has
> > 29 days in leap years, but only 28 otherwise. You exploit that above
> > by checking whether trying to construct "February 29th" raises an
> > exception. That's fine. At least an equally good way is to note that
> > the difference between March 1 and Februrary 28 is 2 days only in a
> > leap year, so:
> > from datetime import date, timedelta
> > def isleap(year):
> > return (date(3, 1, year) - date(2, 28, year)).days == 2
> <SNIP 2 other ways of similar style>
> > def isleap(year):
> > return (date(year+1, 1, 1) - date(year, 1, 1)).days == 366
> > IOW, if you can think of one way to do it with a Boolean expression,
> > it's common to think of more. And, of course, that's the kind of
> > practice that makes it feel natural, over time.
> 4 ways all shorter than mine; well, thank goodness I wasn't asking about
> this in Perl ;-)
> Thanks for the examples. Pretty and concise often go together, but they
> seem not to be want to be seen with me. Implausible though my posting
> history may make it sound, I've done a fair bit of work in set theory
> and math. logic. While my proofs work, they are almost never pretty or
> concise. Seems like my code has similar tendencies. I appreciate the
> pushes in a better direction.
> At least I won't be stuck for things to do when it comes time to refactor!
> Thanks to both,
> Brian vdB
> Tutor maillist - Tutor at python.org
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