With Python's optparse module, how do you create an option that takes a variable number of arguments?

Question

With Perl's Getopt::Long you can easily define command-line options that take a variable number of arguments:

foo.pl --files a.txt             --verbose
foo.pl --files a.txt b.txt c.txt --verbose

Is there a way to do this directly with Python's optparse module? As far as I can tell, the nargs option attribute can be used to specify a fixed number of option arguments, and I have not seen other alternatives in the documentation.

Answer 1

My mistake: just found this Callback Example 6.

Answer 2

I believe optparse does not support what you require (not directly -- as you noticed, you can do it if you're willing to do all the extra work of a callback!-). You could also do it most simply with the third-party extension argparse, which does support variable numbers of arguments (and also adds several other handy bits of functionality).

This URL documents argparse's add_argument -- passing nargs='*' lets the option take zero or more arguments, '+' lets it take one or more arguments, etc.

Answer 3

Wouldn't you be better off with this?

foo.pl --files a.txt,b.txt,c.txt --verbose

Answer 4

This took me a little while to figure out, but you can use the callback action to your options to get this done. Checkout how I grab an arbitrary number of args to the "--file" flag in this example.

from optparse import OptionParser,

def cb(option, opt_str, value, parser):
        args=[]
        for arg in parser.rargs:
                if arg[0] != "-":
                        args.append(arg)
                else:
                        del parser.rargs[:len(args)]
                        break
        if getattr(parser.values, option.dest):
                args.extend(getattr(parser.values, option.dest))
        setattr(parser.values, option.dest, args)

parser=OptionParser()
parser.add_option("-q", "--quiet",
        action="store_false", dest="verbose",
        help="be vewwy quiet (I'm hunting wabbits)")
parser.add_option("-f", "--filename",
        action="callback", callback=cb, dest="file")

(options, args) = parser.parse_args()

print options.file
print args

Only side effect is that you get your args in a list instead of tuple. But that could be easily fixed, for my particular use case a list is desirable.