list in a tuple

[Arnaud Delobelle]

On Dec 24, 4:08 pm, Arnaud Delobelle <arno... at googlemail.com> wrote:
[...]
> class mytuple(tuple):
>     "It's ok to do t[i] = obj as long as t[i] was already obj"
>     def __setitem__(self, i, val):
>         if self[i] is not val:
>             raise TypeError("'mytuple' object is immutable")
>
> So:
>
> >>> a = mytuple(([1], 2))
> >>> a[0] += [3] # This now works
> >>> a[1] += 4   # This won't work as ints are immutable
>
> Traceback (most recent call last):
>   File "<stdin>", line 1, in <module>
>   File "tuple.py", line 4, in __setitem__
>     raise TypeError("'mytuple' object is immutable")
> TypeError: 'mytuple' object is immutable>>> a
>
> ([1, 3], 2)
>
> It wouldn't slow anything down I suppose, just make some currently
> failing code succeed.

Damn! I forgot to finish my post.  I wanted to add that when replacing
the inner list with a tuple, the 'mytuple' will still raise an error
for the reasons explained above:

>>> a = mytuple(((1,), 2))
>>> a[0] += (3,)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "tuple.py", line 4, in __setitem__
    raise TypeError("'mytuple' object is immutable")
TypeError: 'mytuple' object is immutable

--
Arnaud