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

def send(self, request, stream=False, timeout=None, verify=False, cert=None, proxies=None):
        if request.method != 'GET':
            raise HTTPMethodUnavailableError("FTP requests do not support method '%s'" %
                                             request.method, request.method)
        try:
            real_resp = urllib_urlopen(request.url, timeout=timeout)
            # we're going to fake a requests.Response with this
            resp = requests.Response()
            resp.status_code = 200
            resp.url = request.url
            resp.headers = {}
            resp._content = real_resp.read()
            resp.raw = _dummy
            return resp
        except URLError:
            raise FTPError(request.url)

def __init__(self, url):
        message = 'error while retrieving %s' % url
        super(FTPError, self).__init__(message)