Re: Python 2.5: wrong number of arguments given in TypeError forfunction argument aggregation (dictionary input vs the norm)

**M.-A. Lemburg** · Oct 31 '08, 09:35 AM

On 2008-10-31 00:18, John Krukoff wrote:

On Fri, 2008-10-31 at 08:55 +1000, James Mills wrote:

>What you have discovered is not a bug :)
>>
>cheers
>James
>>

>
Are you sure? It looks like his complaint isn't that it doesn't work,
but that the error message is misleading.
>
With the setup:
>
Python 2.5.2 (r252:60911, Sep 22 2008, 12:08:38)
[GCC 4.1.2 (Gentoo 4.1.2 p1.1)] on linux2
Type "help", "copyright" , "credits" or "license" for more information.

>>>def foo( a, b, c ):

... pass
...
>
Compare the error messages from:
>

>>>foo( **{ 'a' : 1, 'c' : 3 } )

Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: foo() takes exactly 3 non-keyword arguments (1 given)
>
to the error message here:
>

>>>foo( **{ 'a' : 1, 'b' : 3 } )

Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: foo() takes exactly 3 non-keyword arguments (2 given)

The (n given) notice refers to the number of keyword parameters
you specified in the call that could be associated with a
non-keyword arguments of the function.

I agree that this is a bit misleading.

Please open a bug report on python.org.

Is it even possible to get an error message in terms of required keyword
arguments? I seem to remember seeing a note about keyword only arguments
recently...

You probably saw PEP 3102:

PEP 3102 – Keyword-Only Arguments | peps.python.org

http://www.python.org/dev/peps/pep-3102/

This PEP proposes a change to the way that function arguments are assigned to named parameter slots. In particular, it enables the declaration of “keyword-only” arguments: arguments that can only be supplied by keyword and which will never be automatic...

That has a somewhat different focus though: it allows defining
keyword-only arguments, ie. ones that cannot be used as
both non-keyword parameter and keyword parameter (like we
have in Python 2.x).

--
Marc-Andre Lemburg
eGenix.com

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