optparse and counting arguments (not options)

[Steven Bethard]

I feel like I must be reinventing the wheel here, so I figured I'd post 
to see what other people have been doing for this.  In general, I love 
the optparse interface, but it doesn't do any checks on the arguments. 
I've coded something along the following lines a number of times:

     class OptionArgParser(optparse.OptionParser):
         def __init__(self, *args, **kwargs):
             self.min_args = kwargs.pop('min_args', None)
             self.max_args = kwargs.pop('max_args', None)
             self.arg_values = kwargs.pop('arg_values', None)
             optparse.OptionParser.__init__(self, *args, **kwargs)

         def parse_args(self, args=None):
             options, args = optparse.OptionParser.parse_args(self, args)
             if self.min_args is not None and len(args) < self.min_args:
                 self.error('too few arguments')
             if self.max_args is not None and len(args) > self.max_args:
                 self.error('too many arguments')
             if self.arg_values is not None:
                 for arg, values in zip(args, self.arg_values):
                     if values is not None and arg not in values:
                         message = 'argument %r is not one of: %s'
                         self.error(message % (arg, ', '.join(values)))
             return options, args

This basically lets me skip some simple checks by creating instances of 
OptionArgParser instead of optparse.OptionParser, and supplying my new 
options:

     parser = OptionArgParser(
         min_args=1, arg_values=[commands],
         usage='%%prog [options] (%s) ...' % '|'.join(commands),
         description='invoke one of the commands')

Is this problem already solved in some module that I've missed?

STeVe