###
6.21.2.9 Putting it all together

Here's what `optparse`-based scripts usually look like:

    from optparse import OptionParser
    [...]
    def main():
        usage = "usage: %prog [options] arg"
        parser = OptionParser(usage)
        parser.add_option("-f", "--file", dest="filename",
                          help="read data from FILENAME")
        parser.add_option("-v", "--verbose",
                          action="store_true", dest="verbose")
        parser.add_option("-q", "--quiet",
                          action="store_false", dest="verbose")
        [...]
        (options, args) = parser.parse_args()
        if len(args) != 1:
            parser.error("incorrect number of arguments")
        if options.verbose:
            print "reading %s..." % options.filename
        [...]

    if __name__ == "__main__":
        main()