Misleading error message of the day

[Benjamin Kaplan]

On Thu, Dec 8, 2011 at 2:09 PM, Ethan Furman <ethan at stoneleaf.us> wrote:
> Benjamin Kaplan wrote:
>>
>> On Thu, Dec 8, 2011 at 1:42 PM, Roy Smith <roy at panix.com> wrote:
>>>
>>> (some,
>>>  very,
>>>  long,
>>>  list,
>>>  of,
>>>  variable,
>>>  names,
>>>  to,
>>>  get,
>>>  the,
>>>  stuff,
>>>  unpacked,
>>>  into) = function_that_should_return_a_14_tuple()
>>>
>>> raises
>>>
>>> ValueError: too many values to unpack
>>>
>>> Quick, what's the bug?  Did I forget a variable on the LHS, or is my
>>> function returning more things than it should?  I know it's supposed to be
>>> 14, but I don't know which side is wrong.  Had it said "... expected 13, got
>>> 14", I would know immediately.
>>>
>>
>> If the RHS was a tuple or a list, yes you could know immediately. But
>> unpacking works with any iterable, so it probably doesn't special-case
>> lists and tuples. Iterables don't have a size- they just keep going
>> until StopIteration is raised. So in EVERY SINGLE CASE, you would get
>> "expected n args, got n+1" even if the iterable would return 24 items
>> instead of 14, or would never stop returning items.
>
>
> Not so.  There could be fewer, in which you could see "expected 13 args, got
> 7."
>

You mean like this?

>>> a,b,c = ['a','b']
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: need more than 2 values to unpack