Is tuple unpacking incompatible with `map'?

[Gordon McMillan]

François Pinard wrote:
> Is it possible that tuple unpacking is not compatible with `map',
> or is there something I do not understand properly?  Here is a
> transcript.  This is with Python 1.5.2.
> 
> >>> def postsort(pair):
> ...	return pair[1]
> ... 
> >>> map(postsort, [(1, 'un'), (2, 'deux'), (3, 'trois')])
> ['un', 'deux', 'trois']
> >>> def postsort(key, item):
> ...	return item
> ... 
> >>> map(postsort, [(1, 'un'), (2, 'deux'), (3, 'trois')])
> Traceback (innermost last):
>   File "<stdin>", line 1, in ?
> TypeError: not enough arguments; expected 2, got 1
> >>>
> 
> Maybe `map' is trying to protect me against errors I'm not doing?
>  I would prefer to use tuple unpacking here, as it allows for
> cleaner writing.

Tuple unpacking is not quite as automatic as you are 
assuming:

>>> def postsort((key, item)):
... 	return item
... 
>>> map(postsort, [(1, 'un'), (2, 'deux'), (3, 'trois')])
['un', 'deux', 'trois']

cats-sank-ly y'rs

- Gordon