from urllib.request import urlretrieveimport sysimport osprev_reported_download_percent = None# 首先定义下载 hook，作为 urllib.request.urlretrive 的关键字参数def download_hook(count, block_size, total_size):    """ 接口是写死的 """    global prev_reported_download_percent    percent = int(count*block_size*100/total_size)    if prev_reported_download_percent != percent:        if percent % 5 == 0:            sys.stdout.write('%s%%' % percent)            sys.stdout.flush()        else:            sys.stdout.write('.')            sys.stdout.flush()        prev_reported_download_percent = percentdef maybe_download(filename, force=False):    """ force 表示是否强制下载 """    if force or not os.path.exists(filename):        print('Attempting to download')        filename, _ = urlretrieve(url+filename, filename, reporthook=download_hook)            # url+filename：表示文件的 url 地址，            # filename 则为保存到本地时的文件名        print('\nDownload completed!')    # statinfo = os.stat(filename)    return filename

比如对于 http://ufldl.stanford.edu/housenumbers/ 网站下的 train.tar.gz/test.tar.gz两文件，客户端的调用方式为：

url = 'http://ufldl.stanford.edu/housenumbers/'train_filename = maybe_download('train.tar.gz')test_filename = maybe_download('test.tar.gz')