En Thu, 07 Feb 2008 16:16:11 -0200, [EMAIL PROTECTED] <[EMAIL PROTECTED]> escribió: > On Feb 7, 11:38 am, [EMAIL PROTECTED] wrote:
> I don't see why you should get either. > > Especially considering this behaviour: > >>>> a=[] >>>> row=[ [] for n in range(0,10) ] >>>> a.extend(row[:]) >>>> a > [[], [], [], [], [], [], [], [], [], []] >>>> a[0].extend(row[:]) >>>> a > [[[...], [], [], [], [], [], [], [], [], []], [], [], [], [], [], [], > [], [], []] Those [...] should give a clue. Usually Python doesn't "shorten" a list representation: if it takes a thousand lines to output a list, there will be a thousand lines of output. The [...] means that the list is *recursive*: it has an element that refers to the list itself, so it can't be represented in the normal way. Why is it recursive? row[:] is a new list, not the same object as row. It is a copy - but a "shallow" copy, because their elements aren't copies themselves. So row[0] is the same object as row[:][0] >>> x = row[:] >>> x == row True >>> x is row False >>> x[0] is row[0] True In the line a[0].extend(row[:]), a[0] is THE SAME LIST as row[:][0], the first item you are appending. That is, the first thing extend() does is conceptually a[0].append(a[0]) - and you got a recursive structure. > Bug in IDLE? No, just a misunderstanding of what [:] does, I presume. -- Gabriel Genellina -- http://mail.python.org/mailman/listinfo/python-list
