def opt_filter(self, my_filter):
        try:
            # Weed out invalid filters
            XPath(my_filter)
        except XPathSyntaxError:
            raise usage.UsageError("Invalid XPath expression: %s" % my_filter)
        self['filters'].append(my_filter)
dataset/ETHPy150Open jdswinbank/Comet/comet/service/broker.py/Options.opt_filter/original