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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 build_opener(self):
 """ Builds url opener, initializing proxy. @return: OpenerDirector """

        http_handler = urllib2.HTTPHandler() # debuglevel=self.transport.debug

        if util.empty(self.transport.proxy_url):
            return urllib2.build_opener(http_handler)

        proxy_handler = urllib2.ProxyHandler(
            {self.transport.proxy_url[:4]: self.transport.proxy_url})

        return urllib2.build_opener(http_handler, proxy_handler)