trapping errors in function call syntax

[Duncan Booth]

Fredrik Lundh wrote:
> Avi Kak wrote:
>> Suppose I write a function that I want to be called
>> with ONLY keyword argumnts, how do I raise an
>> exception should the function get called with
>> what look like position-specfic arguments?
> 
> here's one way to do it:
> 
>>>> def func(*args, **kw):
> ...     def myrealfunc(a=1, b=2, c=3):
> ...             print a, b, c
> ...     if args:
> ...             raise TypeError("invalid call")
> ...     return myrealfunc(**kw)
> ...
> 

If you aren't particular about the message then you can do without the args 
argument and just define it with **kw:

>>> def func(**kw):
     def myrealfunc(a=1, b=2, c=3):
             print a, b, c
     return myrealfunc(**kw)

    
>>> func(1)

Traceback (most recent call last):
  File "<pyshell#14>", line 1, in -toplevel-
    func(1)
TypeError: func() takes exactly 0 arguments (1 given)
>>> func(a=3)
3 2 3
>>> 

and if you are particular about the message perhaps submitting a patch to 
generate a more appropriate message would be a good idea.