[Tutor] tuple/list assignment in 'for-in'

[brian will]

Hi there,

I can't explain my experience with what I like to call 'parallel
assignment' (tuple/list assignment) inside 'for-in' loops and list
comprehensions:

1)
>>> [f + g for f, g in (1, 2), (3, 4)]
[3, 7]

2)
>>> x = 'ab'
>>> y = 'cd'
>>> [f + g for f, g in x, y]
['ab', 'cd']

3)
>>> f, g = '123', '456'
>>> f
'123'
>>> g
'456'

4)
>>> [f + g for f, g in '123', '456']
Traceback (most recent call last):
  File "<pyshell#55>", line 1, in -toplevel-
    [f + g for f, g in '123', '456']
ValueError: too many values to unpack

So why does it accept references to strings but not string literals?
The third example works with a tuple assignment of string literals but
not in the for-in? Any good reason for this, or is it just a quirk?

Thanks,

--Brian Will