Could you explain this rebinding (or some other action) on "nums = nums"?

[Denis McMahon]

On Tue, 01 Dec 2015 03:32:31 +0000, MRAB wrote:

> In the case of:
> 
>      tup[1] += [6, 7]
> 
> what it's trying to do is:
> 
>      tup[1] = tup[1].__iadd__([6, 7])
> 
> tup[1] refers to a list, and the __iadd__ method _does_ mutate it, but
> then Python tries to put the result that the method returns into tup[1].
> That fails because tup itself is a tuple, which is immutable.

I think I might have found a bug:

$ python
Python 2.7.3 (default, Jun 22 2015, 19:33:41) 
[GCC 4.6.3] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> tup = [1,2,3],[4,5,6]
>>> tup
([1, 2, 3], [4, 5, 6])
>>> tup[1]
[4, 5, 6]
>>> tup[1] += [7,8,9]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'tuple' object does not support item assignment
>>> tup[1]
[4, 5, 6, 7, 8, 9]
>>> tup
([1, 2, 3], [4, 5, 6, 7, 8, 9])
>>> quit()

-- 
Denis McMahon, denismfmcmahon at gmail.com