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Testing for presence of arguments

Madhusudan Singh spammers-go-here at spam.invalid
Wed Aug 17 12:08:22 EDT 2005 
Dan Sommers wrote:

> On Wed, 17 Aug 2005 11:13:03 -0400,
> Madhusudan Singh <spammers-go-here at spam.invalid> wrote:
> 
>> I know how to set optional arguments in the function definition. Is
>> there an intrinsic function that determines if a certain argument was
>> actually passed ? Like the fortran 95 present() logical intrinsic ?
> 
>     def f(**kw):
>         if kw.has_key('required_argument'):
>             print "require_argument was present"
>         else:
>             print "require_argument was not present"
> 
>> My required functionality depends on whether a certain argument is
>> specified at all. (Setting default values is *not* good enough.).
> 
> You can very nearly achieve this with carefully planned default
> arguments.  Put this into a module:
> 
>     class _SemiPrivateClass:
>         pass
> 
>     def f(required_argument=_SemiPrivateClass):
>         if required_argument == _SemiPrivateClass:
>             print "required_argument was probably not present"
>         else:
>             print "required_argument was present"
> 
> It's not impossible fool f, but an external module has to try very hard
> to do so.
> 
> (All code untested.)
> 
> Regards,
> Dan
> 

Thanks for the suggestion, but seems needlessly complicated for something
very simple.
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