Steven D'Aprano wrote: > I'm trying to understand the use of tuples in function argument lists. > > I did this: > >>>>def tester(a, (b,c)): > > ... print a, b, c > ... > >>>>tester(1, 2) > > Traceback (most recent call last): > File "<stdin>", line 1, in ? > File "<stdin>", line 1, in tester > TypeError: unpack non-sequence > > That was obvious result. > >>>>tester(1, (2, 3)) > > 1 2 3 > >>>>tester('ab', 'ab') > > ab a b > > And so were those. > > Then I tried this: > >>>>def tester(a, (b,c)=None): > > ... if (b,c) is None: > ... print a, None > ... else: > ... print a, b, c > > Needless to say, it did not do what I expected it to do. I didn't expect > it to either :-) > > I tried looking at the language reference here: > > http://docs.python.org/ref/function.html > > but I can't seem to find anything in their that says that tuples-as-args > are legal. Am I misreading the docs, or is this accidental behaviour that > shouldn't be relied on?
Tuples-as-arg are legal. Tuple-as-keyword, too *if* the default value is something that can actually unpack to a tuple. A default of None is...silly. In : def tester(a, (b,c)=(1,2)): ...: print a,b,c ...: In : tester(1) 1 1 2 Tuple-as-arg is probably pretty safe. Tuple-as-keyword, possibly not-so-much. > Does anyone use this behaviour, and if so, under what circumstances is it > useful? import math def distance((x1,y1), (x2,y2)): return math.sqrt((x2-x1)**2 + (y2-y1)**2) distance(point1, point2) Personally, I prefer to explicitly unpack the tuple in the function body. -- Robert Kern [EMAIL PROTECTED] "In the fields of hell where the grass grows high Are the graves of dreams allowed to die." -- Richard Harter -- http://mail.python.org/mailman/listinfo/python-list