On Dec 28, 1:34 am, "Gabriel Genellina" <[EMAIL PROTECTED]> wrote: > En Thu, 27 Dec 2007 16:38:07 -0300, <[EMAIL PROTECTED]> escribió: > > > > > On Dec 27, 8:20 pm, Wildemar Wildenburger > > <[EMAIL PROTECTED]> wrote: > > >> From that post: > >> > Ok, I do admit that doing > > >> > a = ([1], 2) > >> > a[0].append(2) > > >> > also doesn't throw an error, but this only confuses me more. > > >> Why? You mutate thelist, but thetupledoes not change. It is still > >> atupleof alistand an int. At least that's how I think about it, and I > >> seem to recall reading that beavior justified like this (don't ask me > >> where though (might have been "Dive Into Python", but maybe not)). > > > That part is ok, I mean it doesn't confuse me I just wanted to say > > that this is somewhat confusing behavior. > > I agree that its not best put... But I was thinking about the last > > part of the post, the part > > that talks about trying to print a tuple and getting an error. > > Instead of trying to explain it myself, I'll refer you to this little > essay [1] by Michael Hudson including some nice ASCII art, and a long > reply from Alex Martelli from which I'll quote just a few memorable > paragraphs. (Just replace "dictionary" with "tuple" in your example) > > """There is [...] a huge difference > between changing an object, and changing (mutating) some > OTHER object to which the first refers. > > In Bologna over 100 years ago we had a statue of a local hero > depicted pointing forwards with his finger -- presumably to > the future, but given where exactly it was placed, the locals > soon identified it as "the statue that points to Hotel > Belfiore". The one day some enterprising developer bought > the hotel's building and restructured it -- in particular, > where the hotel used to be was now a restaurant, Da Carlo. > > So, "the statue that points to Hotel Belfiore" had suddenly > become "the statue that points to Da Carlo"...! Amazing > isn't it? Considering that marble isn't very fluid and the > statue had not been moved or disturbed in any way...? > > This is a real anecdote, by the way (except that I'm not > sure of the names of the hotel and restaurant involved -- > I could be wrong on those), but I think it can still help > here. The dictionary, or statue, has not changed at all, > even though the objects it refers/points to may have been > mutated beyond recognition, and the name people know it > by (the dictionary's string-representation) may therefore > change. That name or representation was and is referring > to a non-intrinsic, non-persistent, "happenstance" > characteristic of the statue, or dictionary... > """ > > [1]http://python.net/crew/mwh/hacks/objectthink.html > > -- > Gabriel Genellina
Thank you very much for this discussion and reference [1] and other pointers in [1]. This has definitely helped my understanding of such matters. -- http://mail.python.org/mailman/listinfo/python-list
