How to use the scrapelib.__init__.HTTPError function in scrapelib

headers, self.headers,
            dict_class=requests.structures.CaseInsensitiveDict)
        headers = requests.sessions.merge_setting(
            kwarg_headers, headers,
            dict_class=requests.structures.CaseInsensitiveDict)

        _start_time = time.time()

        resp = super(Scraper, self).request(method, url, timeout=timeout, headers=headers,
                                            **kwargs)
        self.stats['total_requests'] += 1
        self.stats['total_time'] += (time.time() - _start_time)
        self.stats['average_time'] = self.stats['total_time'] / self.stats['total_requests']

        if self.raise_errors and not self.accept_response(resp):
            raise HTTPError(resp)
        return resp

def __init__(self, response, body=None):
        message = '%s while retrieving %s' % (response.status_code, response.url)
        super(HTTPError, self).__init__(message)
        self.response = response
        self.body = body or self.response.text