On 2007-09-13, Ian Clark <[EMAIL PROTECTED]> 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]
It says: You need to read more than the first sentence of a message before responsing: > Well, it would say that if it weren't somewhat buggy. l[:1] > doesn't evaluate to a number, but to a list containing one > number, so the above program doesn't do what you say it does. > > It should read something like: > > def my_sum(seq): > if len(seq) == 0: > return 0 > else: > return seq[0] + my_sum(seq[1:]) -- Neil Cerutti -- http://mail.python.org/mailman/listinfo/python-list
