On 12/8/11 4:21 PM, Chris Angelico wrote:
On Fri, Dec 9, 2011 at 2:55 AM, Andrea Crotti<andrea.crott...@gmail.com> wrote:
Yes but how do you know how many values you generated when it quits?
I mean I don't know how it work internally, but it should keep a temporary
list of the yielded values to be able to find out how many values are
there..
Iterator unpacking works roughly thus:
1) Count up how many results you need (call that N)
2) N times, get a value from the iterator. If StopIteration is raised,
swallow it and raise ValueError because there were too few values.
3) Attempt to get one more value from the iterator. If StopIteration
is NOT raised, raise ValueError because there were too many values.
At no point is the "total size" of the iterator counted (it could,
after all, be infinite). When ValueError is raised, all that's known
is that StopIteration wasn't raised at the end of the process.
unpack_iterable() has the original object available to it, not just the
iterator. It could opportunistically check for __len__() and fall back to the
less informative message when it is absent.
--
Robert Kern
"I have come to believe that the whole world is an enigma, a harmless enigma
that is made terrible by our own mad attempt to interpret it as though it had
an underlying truth."
-- Umberto Eco
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