On Thu, 27 Feb 2014 18:19:09 +0200 Marko Rauhamaa <ma...@pacujo.net> wrote:
> Eric Jacoboni <eric.jacob...@gmail.com>: > > >>>> a_tuple[1] += [20] > > Traceback (most recent call last): > > File "<stdin>", line 1, in <module> > > TypeError: 'tuple' object does not support item assignment > > > > [...] > > > > But, then, why a_tuple is still modified? > > That's because the += operator > > 1. modifies the list object in place > > 2. tries to replace the tuple slot with the list (even though the > list hasn't changed) > > It's Step 2 that raises the exception, but the damage has been done > already. > > One may ask why the += operator modifies the list instead of creating > a new object. That's just how it is with lists. > > BTW, try: > > >>> a_tuple[1].append(20) > >>> a_tuple[1].extend([20]) > > Try also: > > >>> a_tuple[1] = a_tuple[1] > [...] Also try: x = a_tuple[1] #What's in a name? x is a_tuple[1] #Obviously, but: x += [1] #No error a_tuple[1] += [1] #Error Same object, just a different name - but a different result. I get why, but still find that odd. -- John -- https://mail.python.org/mailman/listinfo/python-list
