Determine actually given command line arguments

[Henry Leyh]

On 15.05.2013 16:08, Skip Montanaro wrote:
>> Yes, I was trying that and it sort of works with strings if I use something sufficiently improbable like "__UNSELECTED__" as default.  But it gets difficult with boolean or even number arguments where you just may not have valid "improbable" defaults.  You could now say, so what, it's the default anyway.  But in my program I would like to distinguish between given and not given arguments rather than between default and non-default.
>
> Initialize all your arg variables to None, then after command line
> processing, any which remain as None weren't set on the command line.
> At that point, set them to the actual defaults.  I think that's a
> pretty common idiom.
>
> Note: I am an old cranky dude and still use getopt.  This idiom is
> pretty easy there.  YMMV with argparse or optparse.

Unfortunately, argparse wants to know the type of the argument and the 
boolean arguments (those with action=store_true) can't be initialized 
with None.

However, maybe I could convert boolean arguments to something like

   parser.add_argument('--foo', type=str, nargs='?', const='True', 
default=None)

I'd then have to check for string 'True' rather than for boolean True, 
though.

Regards,
Henry