code: pyhg

ref: 5513dae7d9eee46f7e1843c8eeeaf9066d0ec632
dir: /sys/src/cmd/python/Doc/lib/required_1.py/

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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.verbose
print "file:", options.file
parser.check_required("-f")