option argument length

[Peter Otten]

Ritesh Raj Sarraf wrote:

> My program uses mostly "option arguments" hence my len(args) value is
> always zero. I need to check if the user has passed the correct number of
> "option arguments". Something like:
> 
> (options,args) = parser.parse_args()
> 
> len(options) != 1 or len(options) > 2:
>     print "Incorrect number of arguments passed."
> 
> How do I accomplish it ?

Judging from your code sample invention is the mother of that necessity.
You can pass a custom Values object with a __len__() method

class MyValues:
    def __len__(self):
        return len(self.__dict__)

# ...

options, args = parser.parse_args(values=MyValues())

but you should do your users a favour and give them meaningful error
messages. I can't conceive how you could achieve this by checking the
number of options. Explicit constraint checks like

options, args = parser.parse_args()
if options.eat_your_cake and options.have_it:
    parser.error("Sorry, you cannot eat your cake and have it")

will increase your script's usability and make it easier to maintain for
only a tiny amount of work.

Peter