With Python's Optparse Module, How Do You Create An Option That Takes A Variable Number Of Arguments?

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

Solution 1:

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,

defcb(option, opt_str, value, parser):
        args=[]
        for arg in parser.rargs:
                if arg[0] != "-":
                        args.append(arg)
                else:
                        del parser.rargs[:len(args)]
                        breakifgetattr(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.

Solution 2:

My mistake: just found this Callback Example 6.

Solution 3:

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.

Solution 4:

Wouldn't you be better off with this?

foo.pl--filesa.txt,b.txt,c.txt--verbose

Solution 5:

I recently has this issue myself: I was on Python 2.6 and needed an option to take a variable number of arguments. I tried to use Dave's solution but found that it wouldn't work without also explicitly setting nargs to 0.

def arg_list(option, opt_str, value, parser):
    args = set()
    for arg in parser.rargs:
        if arg[0] == '-':
            break
        args.add(arg)
        parser.rargs.pop(0)
    setattr(parser.values, option.dest, args)

parser=OptionParser()
parser.disable_interspersed_args()
parser.add_option("-f", "--filename", action="callback", callback=arg_list,
                  dest="file", nargs=0)

(options, args) = parser.parse_args()

The problem was that, by default, a new option added by add_options is assumed to have nargs = 1 and when nargs > 0 OptionParser will pop items off rargs and assign them to value before any callbacks are called. Thus, for options that do not specify nargs, rargs will always be off by one by the time your callback is called.

This callback is can be used for any number of options, just have callback_args be the function to be called instead of setattr.