Ian Clark wrote: > Neil Cerutti wrote: >> On 2007-09-13, Gigs_ <[EMAIL PROTECTED]> wrote: >>> Can someone explain me this >>> >>>>>> def f(l): >>> if l == []: >>> return [] >>> else: >>> return f(l[1:]) + l[:1] # <= cant figure this, how is all >>> sum at the end? >> >> In plain English, the above program says: >> >> The sum of the items in list l is zero if the list is empty. >> Otherwise, the sum is the value of the first item plus the sum of >> the rest of the items in the list. > > Am I missing something? What does this have to do with summing? > > >>> def f(l): > ... if l == []: > ... return [] > ... else: > ... return f(l[1:]) + l[:1] > ... > >>> f([1, 2, 3, 4]) > [4, 3, 2, 1] > > Ian
Add it up! Round Sum 0 f([1, 2, 3, 4]) 1 f([2, 3, 4]) + [1] 2 f([3, 4]) + [2] + [1] 3 f([4]) + [3] + [2] + [1] 4 f([]) + [4] + [3] + [2] + [1] Total [] + [4] + [3] + [2] + [1] = [4, 3, 2, 1] James -- http://mail.python.org/mailman/listinfo/python-list
