'Download all category html, can use mthreading'

def download_categories(self):

    category_urls = [c.url for c in self.categories]
    requests = network.multithread_request(category_urls, self.config)
    for (index, _) in enumerate(self.categories):
        req = requests[index]
        if (req.resp is not None):
            self.categories[index].html = network.get_html(req.url, response=req.resp)
        elif self.config.verbose:
            print ('deleting    category', self.categories[index].url, 'due    to    download    err')
    self.categories = [c for c in self.categories if c.html]
