import optparse class OptionParser (optparse.OptionParser):     def check_required (self, opt):        option = self.get_option(opt)         # Assumes the option's 'default' is set to None!        if getattr(self.values, option.dest) is None:            self.error("%s option not supplied" % option)  parser = OptionParser()parser.add_option("-v", action="count", dest="verbose")parser.add_option("-f", "--file", default=None)(options, args) = parser.parse_args() print "verbose:", options.verboseprint "file:", options.fileparser.check_required("-f")