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Re: Misleading error message of the day

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References <roy-9DEDD9.09233308122011@news.panix.com> <jbqil6$esn$1@dough.gmane.org> <mailman.3417.1323357938.27778.python-list@python.org> <18647617.2258.1323358966076.JavaMail.geo-discussion-forums@yqf20> <mailman.3421.1323359453.27778.python-list@python.org> <3164448.1087.1323369765528.JavaMail.geo-discussion-forums@yqcm37> <CAMuTYXhG-+CVm1BC5TKr2ektgPN1KC2BnbLXMy+X_Z-GrWMotg@mail.gmail.com> <4EE10B63.2010600@stoneleaf.us>
Date Thu, 8 Dec 2011 14:38:28 -0500
Subject Re: Misleading error message of the day
From Benjamin Kaplan <benjamin.kaplan@case.edu>
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On Thu, Dec 8, 2011 at 2:09 PM, Ethan Furman <ethan@stoneleaf.us> wrote:
> Benjamin Kaplan wrote:
>>
>> On Thu, Dec 8, 2011 at 1:42 PM, Roy Smith <roy@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

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Thread

Misleading error message of the day Roy Smith <roy@panix.com> - 2011-12-08 09:23 -0500
  Re: Misleading error message of the day Andrea Crotti <andrea.crotti.0@gmail.com> - 2011-12-08 14:39 +0000
  Re: Misleading error message of the day Chris Angelico <rosuav@gmail.com> - 2011-12-09 01:40 +1100
  Re: Misleading error message of the day Robert Kern <robert.kern@gmail.com> - 2011-12-08 14:47 +0000
    Re: Misleading error message of the day Roy Smith <roy@panix.com> - 2011-12-08 07:30 -0800
      Re: Misleading error message of the day Tim Chase <python.list@tim.thechases.com> - 2011-12-08 11:41 -0600
    Re: Misleading error message of the day Roy Smith <roy@panix.com> - 2011-12-08 07:30 -0800
  Re: Misleading error message of the day Jean-Michel Pichavant <jeanmichel@sequans.com> - 2011-12-08 16:03 +0100
    Re: Misleading error message of the day Roy Smith <roy@panix.com> - 2011-12-08 07:33 -0800
      Re: Misleading error message of the day Jean-Michel Pichavant <jeanmichel@sequans.com> - 2011-12-08 20:49 +0100
      Re: Misleading error message of the day Ethan Furman <ethan@stoneleaf.us> - 2011-12-08 12:13 -0800
      Re: Misleading error message of the day Lie Ryan <lie.1296@gmail.com> - 2011-12-09 12:46 +1100
        Re: Misleading error message of the day alex23 <wuwei23@gmail.com> - 2011-12-08 20:57 -0800
          Re: Misleading error message of the day Lie Ryan <lie.1296@gmail.com> - 2011-12-11 10:41 +1100
      Re: Misleading error message of the day Jean-Michel Pichavant <jeanmichel@sequans.com> - 2011-12-09 11:03 +0100
        Re: Misleading error message of the day Roy Smith <roy@panix.com> - 2011-12-09 09:43 -0500
      Re: Misleading error message of the day Ethan Furman <ethan@stoneleaf.us> - 2011-12-09 09:39 -0800
    Re: Misleading error message of the day Roy Smith <roy@panix.com> - 2011-12-08 07:33 -0800
      Re: Misleading error message of the day Grant Edwards <invalid@invalid.invalid> - 2011-12-08 18:10 +0000
        Re: Misleading error message of the day alister <alister.ware@ntlworld.com> - 2011-12-08 20:58 +0000
          Re: Misleading error message of the day Chris Angelico <rosuav@gmail.com> - 2011-12-09 08:17 +1100
        Re: Misleading error message of the day Roy Smith <roy@panix.com> - 2011-12-08 20:19 -0500
        Re: Misleading error message of the day Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-12-09 02:07 +0000
          Re: Misleading error message of the day Chris Angelico <rosuav@gmail.com> - 2011-12-09 14:46 +1100
            Re: Misleading error message of the day Roy Smith <roy@panix.com> - 2011-12-08 23:44 -0500
  Re: Misleading error message of the day Heiko Wundram <modelnine@modelnine.org> - 2011-12-08 16:16 +0100
    Re: Misleading error message of the day Roy Smith <roy@panix.com> - 2011-12-08 07:42 -0800
      Re: Misleading error message of the day Heiko Wundram <modelnine@modelnine.org> - 2011-12-08 16:50 +0100
        Re: Misleading error message of the day Roy Smith <roy@panix.com> - 2011-12-08 10:42 -0800
          Re: Misleading error message of the day Benjamin Kaplan <benjamin.kaplan@case.edu> - 2011-12-08 13:57 -0500
          Re: Misleading error message of the day Ethan Furman <ethan@stoneleaf.us> - 2011-12-08 11:09 -0800
          Re: Misleading error message of the day Benjamin Kaplan <benjamin.kaplan@case.edu> - 2011-12-08 14:38 -0500
          Re: Misleading error message of the day Ethan Furman <ethan@stoneleaf.us> - 2011-12-08 12:09 -0800
        Re: Misleading error message of the day Roy Smith <roy@panix.com> - 2011-12-08 10:42 -0800
      Re: Misleading error message of the day Andrea Crotti <andrea.crotti.0@gmail.com> - 2011-12-08 15:55 +0000
      Re: Misleading error message of the day Chris Angelico <rosuav@gmail.com> - 2011-12-09 03:21 +1100
      Re: Misleading error message of the day Robert Kern <robert.kern@gmail.com> - 2011-12-08 19:57 +0000
    Re: Misleading error message of the day Roy Smith <roy@panix.com> - 2011-12-08 07:42 -0800

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