<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _get_request_url(self, instance, url):
 """ Get the request address, build with proxy if necessary """

        parsed = urlparse(url)

        _url = url
        if not (parsed.netloc and parsed.scheme) and is_affirmative(instance.get('spark_proxy_enabled', False)):
            master_address = self._get_master_address(instance)
            _url = urljoin(master_address, parsed.path)

        self.log.debug('Request URL returned: %s', _url)
        return _url