On Wed, May 25, 2011 at 9:46 PM, Uncle Ben <bgr...@nycap.rr.com> wrote: > In playing with lists of lists, I found the following: > > (In 3.1, but the same happens also in 2.7) > > list = [1,2,3] > list.append ( [4,5,6] )
Note the lack of output after this line. This indicates that list.append([4,5,6]) returned None. Contrast this with, say, list.pop(). > x = list > x -> > [1,2,3,[4,5,6]] > as expected. > > But the shortcut fails: > > list=[1,2,3] > x = list.append( [4,5,6] ) > x -> > nothing > > Can someone explain this to me? The append() method does *not* return the now-appended-to list. It is a mutator method that modifies the list object in-place; per convention, it therefore returns None to reinforce its side-effecting nature to the user (the interactive interpreter by default does not display None expression results); analogous methods in other languages return void. list.remove(), list.sort(), and list.extend() similarly return None rather than the now-modified list. Cheers, Chris -- http://rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
