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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _get_xml(self, metric):
 """Returns the channel element of the RSS feed"""

        self._opener = urllib2.build_opener()
        self._opener.addheaders = [('User-agent', self.user_agent)]

        if metric:
            url = self.base_url + '?w={0}&u=c'.format(self.woeid)
        else:
            url = self.base_url + '?w={0}'.format(self.woeid)

        return etree.parse(
            self._opener.open(url)
        ).getroot()[0]