How to do *args, **kwargs properly

[Max M]

Lasse Vågsæther Karlsen wrote:
> I must be missing something but what is the proper way to do a function 
> using such arguments ?

> - ability to take an unspecified number of "positional arguments"

You should probably pass a sequence to the method instead. You can do it 
the other way, but it's poor coding style in most cases.


> - ability to take optional named arguments that follows the first arguments

Setting the default value to a value that cannot exist as an argument is 
the normal way. Eg. None.

def fn(vals, cmp=None)


> - raise appropriate errors if I use the wrong named arguments

def fn(*values, cmp=None):
     if cmp is None:
         raise TypeError, "'%s' is an invalid keyword argument for this 
function" % key


If you insist on doing it the other way:

FN_LEGAL_ARGS = set( ('cmp',) )

def fn(*values, **options):
     for key in options.keys():
         if not key in FN_LEGAL_ARGS:
             raise TypeError, "'%s' is an invalid keyword argument for 
this function" % key


-- 

hilsen/regards Max M, Denmark

http://www.mxm.dk/
IT's Mad Science