If you write any command-line tools that have a need for a help message, then you should really try docopt, which gets you out of having to write argument-parsing code yourself. I’ve mentioned it before, briefly, and I wouldn’t want to be without it.

For an example I’m going to pick on Dr Drang, who was unfortunate enough to post such a script recently. Sorry!

Take a look at his original help message, and then check out the following:

Return NCDC weather report for the given date.

Usage: ncdc [options] DATE

    -a, --ascii        : return ASCII file instead of HTML
    -d, --daily        : return daily summary instead of hourly reports
    -m, --month        : entire month, not just a single day
    -p, --precip       : precipitation (hourly only, overrides -d)
    -s, --station STA  : the station abbreviation [default: ORD]
                         O'Hare     ORD
                         Midway     MDW
                         Palwaukee  PWK
                         Aurora     ARR
                         Waukegan   UGN
                         Lewis      LOT
                         DuPage     DPA
                         Lansing    IGQ
                         Joliet     JOT
                         Kankakee   IKK
                         Gary       GYY
    -h, --help         : print this message

It’s essentially the same, but with a couple of minor changes:

  • The description of the script comes before the usage.
  • The date argument is now in upper case.
  • I’ve added long options to make things a little more readable.
  • The description of the station option gains [default: ORD], which specifies — shocker — the default value for that option.

And here’s the new argument-handling code, to replace lines 54–87 in his script (there’s also the new line from docopt import docopt earlier on):

# Handle options.
args = docopt(help)
sta = args['--station'].upper()
ascii = args['--ascii']
month = args['--month']
precip = args['--precip']
daily = False if precip else args['--daily']

d = parse(args['DATE'], dayfirst=False)

Provide docopt with your help message and you get back a dictionary. Options that take an argument give you back the argument, the default or None (if you don’t set a default). The switch-type options are booleans, being False if they’re not used.

Calling the script incorrectly prints the basic usage pattern, and docopt gives you the help options for free. (You don’t have to include them in the help message, even, but you should.)